SCIENCE CLASS 10
CHAPTER -1 CHEMICAL REACTION AND EQUATIONS

QUESTION 1.

    Which of the statements about the reaction below are incorrect?

          2PbO(s) + C(s) → 2Pb(s) + CO22(g)
(a)Lead is getting reduced.
(b)Carbon dioxide is getting oxidised.
(c)Carbon is getting oxidised.
(d)Lead oxide is getting reduced.
(i)(a) and (b)                             (ii)(a) and (c)
(iii)(a), (b) and (c)                    (iv)all

ANSWER

(i)(a) and (b)

QUESTION 2.

Fe2O3 + 2Al → Al2O3 + 2Fe
The above reaction is an example of a
(a)combination reaction.
(b)double displacement reaction.
(c)decomposition reaction.
(d)displacement reaction.

ANSWER

(d)displacement reaction.

QUESTION 3.

What happens when dilute hydrochloric acid is added to iron fillings? Tick the
correct answer.
(a)Hydrogen gas and iron chloride are produced.
(b)Chlorine gas and iron hydroxide are produced.
(c)No reaction takes place.
(d)Iron salt and water are produced.

ANSWER

(a)Hydrogen gas and iron chloride are produced.

QUESTION 4.

What is a balanced chemical equation? Why should chemical equations be
balanced?

ANSWER

A reaction has equal number of atoms of all elements on the both side. This is called a balanced chemical equation. The law of conservation of mass states that mass can neither be created nor destroyed. So, the total mass of the elements present in the products of a chemical reaction should be equal to the total mass of all the elements present in the reactants. In other words, the number of atoms of each element in the product must be equal to the number of atoms of these elements in the reactants.

QUESTION 5.

Translate the following statements into chemical equations and then balance them.
(a)Hydrogen gas combines with nitrogen to form ammonia.
(b)Hydrogen sulphide gas burns in air to give water and sulpur dioxide.
(c)Barium chloride reacts with aluminium sulphate to give aluminium chloride
and a precipitate of barium sulphate.
(d)Potassium metal reacts with water to give potassium hydroxide and hydrogen
gas.

ANSWER

(a) 3H2 + N2 -------- 2NH3
(b) 2H2S + 3O2 ------- 2H2O + 2SO2
(c) 3BaCl2 + Al2(SO4)3 ----------- 2AlCl3 + 3BaSO4
(d) 2K + 2H2O ----------- 2KOH + H2

QUESTION 6.

Balance the following chemical equations.
(a)HNO3 + Ca(OH)2 → Ca(NO3)2 + H2O
(b)NaOH + H2SO4 → Na2SO4 + H2O
(c)NaCl + AgNO3 → AgCl + NaNO3
(d)BaCl2 + H2SO4 → BaSO4 + HCl

ANSWER

(a)2HNO3 + Ca(OH)2 → Ca(NO3)2 + 2H2O
(b)2NaOH + H2SO4 → Na2SO4 + 2H2O
(c)NaCl + AgNO3 → AgCl + NaNO3
(d)BaCl2 + H2SO4 → BaSO4 + 2HCl

QUESTION 7.

Write the balanced chemical equations for the following reactions.
(a)Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water
(b)Zinc + Silver nitrate → Zinc nitrate + Silver
(c)Aluminium + Copper chloride → Aluminium chloride + Copper
(d)Barium chloride + Potassium sulphate → Barium sulphate + Potassium chloride

ANSWER

(a) Ca(OH)2 + CO2 ------------ CaCO3 + H2O
(b) Zn + 2AgNO3 --------------- Zn(NO3)2 + 2Ag
(c) 2Al + 3CuCl2 --------------- 2AlCl3 + 3Cu
(d) BaCl2 + K2SO4 -------------- BaSO4 + 2KCl

QUESTION 8.

Write the balanced chemical equation for the following and identify the type of
reaction in each case.
(a)Potassium bromide(aq) + Barium iodide(aq) → Potassium iodide(aq) +
Barium bromide(s)
(b)Zinc carbonate(s) → Zinc oxide(s) + Carbon dioxide(g)
(c)Hydrogen(g) + Chlorine(g) → Hydrogen chloride(g)
(d)Magnesium(s) + Hydrochloric acid(aq) → Magnesium chloride(aq) + Hydrogen(g)

ANSWER

(a) 2KBr + BaI2 --------------- 2KI + BaBr2
(b) ZnCO3 ---------- ZnO + CO2
(c) H2 + Cl2 ------------ 2HCl
(d) Mg + 2HCl ----------- MgCl2 + H2

QUESTION 9.

What does one mean by exothermic and endothermic reactions? Give examples.

ANSWER

Chemical reaction that release energy in the form of heat, light, or sound are called exothermic reaction.
EXAMPLE : When carbon burns in oxygen to form carbon dioxide, a lot of heat is produced in this reaction :
      C + O2 ------------ CO2 + Heat

Reaction that absorb energy or require energy, in order to proceed are called endothermic reactions.
EXAMPLE : In the process of photosynthesis, plant use the energy from the sun to convert carbo dioxide and water to glucose and oxygen.
    6CO2 + 6H2O ---------- C6H12O6 + 6O2

QUESTION 10.

Why is respiration considered an exothermic reaction? Explain.

ANSWER

Respiration is considered an exothermic reaction because energy is released in this process. During respiration, glucose combines with oxygen of air in the cells of our body to form carbon dioxide and water, and energy is released :
      C6H12O6 + 6O2 ------------ 6CO2 + 6H2O + Energy

QUESTION NO. 11.

Why are decomposition reactions called the opposite of combination reactions?
Write equations for these reactions.

ANSWER

The decomposition reactions are called the opposite of combination reaction because in a decomposition reaction a compound is broke down to form two or more substance whereas in a combination reaction two or more substances combine to form a single substance.
(a) When acidified water is electrolysed, hydrogen and oxygen are formed :
             2H2O -------------------- 2H2 + O2
(b) When hydrogen burns in oxygen, it forms water :
            2H2 + O2 --------------------- 2H2O

QUESTION 12.

 Write one equation each for decomposition reactions where energy is supplied in
the form of heat, light or electricity.

ANSWER

(a) When calcium carbonate is heated, it decompose to form calcium oxide and carbon dioxide :
             CaCO3 ----------------- CaO + CO2
(b) When silver chloride is exposed to sunlight, it decomposes to form silver metal and chlorine gas :
             2AgCl -------------------- 2Ag + Cl2
(c) When acidified water is electrolysed, it decomposes to form hydrogen and oxygen:
             2H2O -------------------- 2H2 + O2

QUESTION 13.

 What is the difference between displacement and double displacement reactions?
Write equations for these reactions.

ANSWER

In a displacement reaction, a more reactive element displaces a less reactive element from its compound whereas in a double displacement reaction, two compounds combine by an exchange of ions to form two new compounds.
(a) A displacement reaction takes place between copper sulphate solution and zinc to form zinc sulphate solution and copper :
       CuSO4 + Zn -------------------- ZnSO4 + Cu
(b) A double displacement reaction takes place between barium chloride solution and sodium sulphate solution to form a white precipitate of barium chloride solution :
       BaCl2 + Na2SO4 ------------------ BaSO4 + 2NaCl

QUESTION 14.

 In the refining of silver, the recovery of silver from silver nitrate solution involved
displacement by copper metal. Write down the reaction involved.

ANSWER

2AgNO3 + Cu --------------------- Cu(NO3)2 + 2Ag

QUESTION 15.

 What do you mean by a precipitation reaction? Explain by giving examples.

ANSWER

A reaction in which an insoluble solid is formed is called a precipitation reaction.
FOR EXAMPLE :  Barium chloride reacts with aluminium sulphate to give aluminium chloride and a precipitate of barium sulphate.
            3BaCl2 + Al2(SO4)3 ---------------  2AlCl3 + 3BaSO4

QUESTION 16.

 Explain the following in terms of gain or loss of oxygen with two examples each.
(a)Oxidation
(b)Reduction

ANSWER

(a) OXIDATION :
     The gain of oxygen by a substance in a reaction is called oxidation.
(i) CO2 + H2 ------------ CO + H2O
(ii) 2Cu + O2 ------------- 2CuO

(b) REDUCTION :
     The loss of oxygen by a substance in a reaction, is called reduction.
(i) CO2 + H2 --------------- CO + H2O
(ii) CuO + H2 -------------- Cu + H2O

QUESTION 17.

 A shiny brown coloured element ‘X’ on heating in air becomes black in colour.
Name the element ‘X’ and the black coloured compound formed.

ANSWER

The shiny brown coloured element X is copper metal (Cu). When copper metal is heated in air, it forms a black coloured compound copper oxide. So, the black coloured compound is copper oxide or copper (II) oxide, CuO.

QUESTION 18.

 Why do we apply paint on iron articles?

ANSWER

The paint is applied on iron articles to prevent their rusting. When a coat of paint is applied to the surface of an iron article, then air and moisture cannot come in contact with the metal of the article and hence no rusting takes place.

QUESTION 19.

 Oil and fat containing food items are flushed with nitrogen. Why?

ANSWER

The plastic bags containing oil and fat containing food items are flushed with an unreactive gas  nitrogen so as to prevent them from getting oxidised and turn rancid. This is because in the presence of oxygen of air, the fats and oils present in food items get oxidised forming product having unpleasant smell and taste which turn the foods rancid. When air containing oxygen is replaced by unreactive nitrogen gas, the packed food items do not get spoiled. They remain fresh for a much longer time.

QUESTION 20.

 Explain the following terms with one example each.
(a)Corrosion

(b)Rancidity

ANSWER

(a)Corrosion :

     Corrosion is defined as a process where materials, usually metals, deteriorate as a result of a chemical reaction with air, moisture, chemicals, etc. For example - iron, in the presence of moisture, reacts with oxygen to form hydrated iron oxide.
         This hydrated iron oxide is rust.

(b)Rancidity :

     The process of oxidating of fats and oils that can be easily noticed by the change in the taste and smell is know as rancidity.
   For example - the taste and smell of butter changes when kept for long. Rancidity can be avoided by :

1. Storing food in air tight containers.
2. Storing food in refrigerators.
3. Adding antioxidants.
4. Storing food in an environment of nitrogen.

CLASS - 10 SCIENCE IMPORTANT QUESTIONS OF MARK 5   FOR BOARD EXAMINATION

QUESTION NO. 15

(a) With the help o suitable circuit diagram prove that the reciprocal of equivalent resistance of a group of resistances joined in a parallel is equal to the sum of the reciprocals of the individual resistances.

(b) In an electric circuit two resistors of 12 ohm are joined in parallel to a 6V battery. Find the current drawn from the battery.

ANSWER NO. 15 

There resistors R1, R2 and R3 are connected in parallel.
The total current I, is equal to the sum the separated currents through each resistor R1, R2 and R3.

I = I1 + I2 + I3           ----------------------------(1)

  Let Rp be the equivalent resistance of the parallel combination of resistors. By applying ohm's law to the parallel combination of resistors.
                 I = V/Rp                (V = IR)
  On applying ohm's law to each resistors, we have 
  I1 = V/R1  ,  I2 = V/R2  and I3 = V/R3    -------------------(2)
         From equation (1) and (2) -
V/Rp = V/R1 + V/R2 + V/R3
V(1/Rp) = V(1/R1 + 1/R2 + 1/R3)
   1/Rp =1/R1 + 1/R2 +1/R3

Thus the reciprocal of the equivalent resistance of a group of resistances joined in parallel is equal to the sum of the reciprocals of individual resistances.

(b) Total resistance in the circuit 1/R = 1/R + 1/R            =  1/12 + 1/12
    1/R = 2/12
    1/6 = 1/6
    R = 6 ohm
R = 6 ohm, V  =6 volt
V/I = R , IR = V , I = V/R = 6/6 = 1 ampere
current drawn by the battery = 1 ampere.

QUESTION NO. 16

What is a solenoid ? Draw the pattern of magnetic field lines of.

(i) A current carrying solenoid and

(ii) A bar magnet

List two distinguishing features between the two fields.

ANSWER NO. 16

SOLENOID

A solenoid is a generic term for a coil of wire used as an electromagnet. It also refers to any device that convert electrical energy to mechanical energy using a solenoid. The device creats a magnetic field from electric current.

(i) The magnetic field for the current carrying solenoid.

(ii) FOR BAR MAGNET

1. The poles of the bar magnet do not lie exactly at end of the magnet but are somewhat inside. In a solenoid, poles can be considered to be lying at the edge. 
2.  The magnetism retains in the bar magnet naturally but in the solenoid, the magnetism is there so long current flows through it.

CLASS - 10 SCIENCE IMPORTANT QUESTIONS OF MARK 5   FOR BOARD EXAMINATION

QUESTION NO. 17

An electric lamp of resistance 20 ohm and a conductor of resistance 4 ohm are connected to 6V battery as shown in the circuit.

(a) the total resistance of the circuit
(b) the current through the circuit
(c) the potential difference across the 
     (i) electric lamp
     (ii) conductor
(d) power of the lamp.

ANSWER NO. 17

(a) Voltage of battery V = 6 volt
Resistance of electric lamp R1 = 20 ohm
Resistance of conductor   = 4 ohm
 Total resistance  R = R1 + R2
                                     = 20 + 4 = 24 ohm
(b) According to ohm's law = V = IR
                                                I = V/R
                                                  = 6/24 = 0.25 ampere
(c) (i) Potential difference across the electric lamp.
    V = IXR1 = 0.25 X 20 = 5 volt.
(ii) Potential difference across the conductor
   V = IXR2 = 0.25 X 4 = 1 volt
(d) Power of lamp = P = VI
                                         = 5 X 0.25 = 1.25 watt.

QUESTION NO. 18

(a) Three resistors of resistances R, R, R are connected.
    (i) in series and
    (ii) in parallel

  write expression for the equivalent ree of the combination in each case.
(b) Two identical  resistors of 12 ohm each are connected to a battery of 3V. Calculate the ratio of the power consumed by the resulting combinations with minimum resistance and maximum resistance.

ANSWER NO. 18

(a) (i) Equivalent resistance R = R1 + R2 + R3
(ii) Equivalent resistance 1/R = 1/R1 +1/R2 + 1/R3

(b) Since resistance are identical of 12 ohm so 
   R = R1 + R2
       = 12 + 12 = 24 ohm
Applied voltage is given V = 3V
  P1 = vv/R = 3X3/2X2 = 9/24 W
If connected in parallel 
1/R = 1/R1 + 1/R2 = 1/12 + 1/12 = 2/12 = 1/6
      R = 6 ohm
 P2 = vv/R = 3X3/6 = 9/6 W
Ratio of power consumed in the two combination is.

    P1/P2 = 9/24  =1/4
              9/6
   P1 : P2 = 1 : 4

CLASS - 10 SCIENCE IMPORTANT QUESTIONS OF MARK 5   FOR BOARD EXAMINATION

QUESTION NO. 13

Compare the power used in 2 ohm resistor in each of the circuit.

ANSWER NO. 13

(i) Potential difference  V = 6 V
Since 1 ohm and 2 ohm resistance are connected in series hence, equivalent resistance of the circuit
       R = 1 + 2 = 3 ohm
According to ohm's law - 
 V = IR,  I = V/R = 6/3 = 2A
Power used in 2 ohm resistance 
= P = IIR = 2X2X2 = 8 watt

(ii) Since 1 ohm and 2 ohm resistors are connected in parallel.
The voltage across each component of a parallel circuit remains the same. Hence the voltage across 2 ohm resistor will be 4V.
 Power consumed by 2 ohm resistor is
 P = VV/R 
     = 4X4/2
     = 8 watt

QUESTION NO. 14

(a) Name and state the rule to determine the direction of force experienced by the a current carrying straight conductor placed in a uniform magnetic which is perpendicular to it. 

(b) Draw a labelled diagram of an electric motor.

ANSWER NO. 14

(a) The left hand rule that was given by Fleming.
 In this rule middle finger shows direction of the current. Fore finger shows direction of magnetic field and thumb shows direction of motion.

(b) 

PRINCIPLE  OF AN ELECTRIC MOTOR

An electric motor works on the principle that when a rectangular coil is placed in a magnetic field and a current passed through it, a force acts on the coil which rotes it continuously.

CLASS - 10 SCIENCE IMPORTANT QUESTIONS OF MARK 3  FOR BOARD EXAMINATION

QUESTION NO. 55

A coil of insulated copper wire is connected to a galvanometer. What would happen if a strong bar magnet is.

(a) Pushed into the coil ?

(b) Withdrawn from inside the coil ?

(c) Held stationary inside the coil ?

 Give justification for each observation.

ANSWER NO. 55

(a) When a bar magnet is pushed into the coil of insultated copper wire connected to a galvanometer, an induced current is set u in the coil due to change of magnetic field through it. As a result, galvanomter gives a deflection.

(b) When the bar magnet is withdrawn from inside the col, again an induced current is setup in the coil due to change of magnetic field through it . As a result galvanometer gives a deflection in the reverse direction.

(c) If the bar magnet is held stationary inside the coil, then there is no induced current in the coil, because there is no change in magnetic field through it. So, galvanometer does not show any deflection.

QUESTION NO. 56

Two circular coil P and Q are kept close to each other, of which coil P carries a current. What will you observe in the galvanometer connected across the coil Q.

(a) if current in the coil P is changed ?

(b) if both the coils are moved in the same direction with the same speed.

ANSWER NO. 56

(a) When current in P is changed, the field associated with coil Q will vary causing an induced current Q, and the galvanometer will be deflected.

(b) If both the coils are moved in the same direction with same speed, there will not be any change in the field associated with Q. Hence no current will be induced in Q. Hence there will be no any deflection in galvanometer.

CLASS - 10 SCIENCE IMPORTANT QUESTIONS OF MARK 5   FOR BOARD EXAMINATION

QUESTION NO. 7

(i) write the step involved in the extraction of pure metal in the middle of activity series from their carbonate ore.

(ii) how is copper extracted from its sulphide Ore? Explain the various steps supported by chemical equation.

(iii) explain the process of electrolytic refining of copper.

ANSWER NO.7

(i) the metals in the middle of the activity series such as iron, lead and copper are moderately reactive. These are usually presented as sulphide or carbonate in nature.
         Carbonate Ores are changed into oxides by heating strongly in limited air. This process is known as calcination of the chemical reaction of calcination of carbonate ore are as follows -
     ZnCO3 ------------------> ZnO + CO2
              The metal oxide are then reduced to metal by using suitable reducing agent such as copper, when zinc oxide is heated with carbon, it is reduced to metallic zinc.
        ZnO + C ------> Zn + CO

(ii) which is found as cu2s in nature can be obtained from its Ore by heating in air.
       2Cu2S + 3O ---------------> 2CuO + 2SO2
       2CuO + 2Cu2S --------> 6Cu + SO2

(iii) copper is refined electrolytically. In this process the impure metal is made at the anode and a thin strip of pure metal is made at cathode. A solution of the metal salt is used as electrolyte. On passing the current through the electrolyte, the pure metal from the anode dissolve into the electrolyte. And equivalent amount of pure metal from the electrolyte is deposit on the cathode. The soluble impurities goes into the solution, where as the insoluble impurities settled down at the bottom of the anode and have known as anode mud.

QUESTION NO.8

Write the chemical formula and name of compound is the active ingredient of all the alcoholic drinks. List its two uses. Write chemical equation and name of the product formed when this compound reacts
(i) sodium metal 
(ii) hot concentrated sulphuric acid.

ANSWER NO.8

Ethanol is a liquid at room temperature. It is commonly called alcohol and it is the active ingredient of all alcoholic drinks.
           Chemical Name - Ethanol
           Chemical formula - CH3CH2OH

UESES

• Because it's good property of solvent it is used in cough syrup, tincture iodine etc
• Used as fuel. Ethanol burns cleanly to form carbon dioxide and water.

REACTION WITH SODIUM 

    2Na + 2CH3CH2OH -----------> 2CH3CH2Na + H2

REACTION WITH HOT CONCENTRATED SULPHURIC ACID

 CH3CH2OH ----------------> CH2 = CH2 + H2O

Reaction gives unsaturated hydrocarbon. Heating ethanol at 443K with excess concentrated sulphuric acid result in ethene.

CLASS - 10 SCIENCE IMPORTANT QUESTIONS OF MARK 5   FOR BOARD EXAMINATION

QUESTION NO.9

(a) List four characteristics of the image formed by plane mirrors.

(b) A 50 cm tall object is placed at a distance of 20 cm from a concave mirror of focal length 30 cm. Use mirror formula to determine position and size of the image formed.

ANSWER  NO.9

(a) 

1. Image is virtual and erect.
2. The size of the image is equal to that of the object.
3. The image formed is as far behind the mirror as the object is in front of it.
4. The image is laterally inverted.

(b) Height of object = 5 cm

       u = - 20 cm

       f = - 30 cm

  Using mirror formula

      1/f = 1/v + 1/u

     1/- 30 = 1/v + 1/- 20

     1/-30 - 1/-20 = 1/v

     1/-30 + 1/20 = 1/v

      -2+3/60 = 1/v

     1/60 = 1/v

     v= 60 cm

   The image of formed 60 cm on the back side of the mirror.

     The height of the image is

       m= h'/h = - v/u

       h'/5 = -60/-20 => 3

       h' = 15 cm

  Hence the image is virtual and height of the image is 15 cm.

QUESTION NO.10

Bulb is rated 41W, 220 volt. Find the current drawn by it, when it is connected to a 220 volt supply. Also find its resistance. If the giving bulb is replaced by a bulb of ratings 25 Watt, 220 volt then there be any change in the value of current and resistance? Justify your answer and determine the change.

ANSWER NO.10

 CASE I

   Power of bulb P = 40 W

   Voltage supplied across the bulb V = 220 V

   P = vi

   i = P/V = 40/220 = 0.18 A

    Resistance of bulb

    P = v.v/R = R =v.v/P = 220X220/40
      = 1210 ohm

CASE II
 Power of bulb  P = 25 walt
                       v = 220 volt
          P = vi
           i = P/v = 25/220
             = 0.1136 
    Resistance of bulb
    P = v.v/R' 
    R' = v.v/P = 220X220/25
       = 1936 ohm

When bulb will change, the current and resistance will be changed.
Changed in current = 0.18 - 0.1136
                                      = 0.0664 A
( current decrease when we use 25 watt bulb in place of 40 watt bulb.)
Changed in resistance  1936 ohm - 1210 ohm = 726 ohm
( Resistance increase when we use 25 watt bulb in place of 40 watt)

CLASS - 10 SCIENCE IMPORTANT QUESTIONS OF MARK 3  FOR BOARD EXAMINATION

QUESTION NO. 45

What is the cause of dispersion of white light through glass prism ? Draw a ray diagram to show the path of light when two indentital glass prism are arranged together in inverted position with respect to each other and a narrow beam of white light is allowed to fall obliquely on one of the faces of the prism.

ANSWER NO. 45

DISPERSION 

The splitting of light into its component colour is called dispersion.

CAUSES OF DISPERSION OF LIGHT

When light passes through a prism, the different frequencies of light travel at different velocities. Because of refraction, the different velocities make the angle of refraction different, causing the light to travel in slightly different direction.

QUESTION NO. 46

Write the function of the following in human eye.
 (i) Cornea
(ii) Retina
(iii) Iris

ANSWER NO. 46

(i) CORNEA

 Light enters the eye through a thin membrane called cornea.

(ii) RETINA

 It is the light sensitive part of the eye on which image is formed by the lens and send impulses to the brain via optive nerve.

(iii) IRIS

  Iris is a dark muscular diaphragm that controls the size of the pupil.

QUESTION NO. 47

What is atmospheric refraction ? Explain why the position of a star as seen by us is not its true position.

ANSWER NO. 47

When the light rays pass through the atmosphere having layers of different densities and refractices then refraction of light takes place. This refraction of light by the earth's atmosphere is called atmospheric refraction.
      The starlight, on entering the earth's atmosphere, undergoes refraction continuously before it reaches the earth. The atmospheric refraction occurs in a medium of gradually changing refractive index. Since the atmosphere bends starlight towards the normal, the apparent position of the star is slightly different from it actual position. The star appears slightly higher than it's actual position when viewed near the horizon.

QUESTION NO. 48

State the difference in colours of the sun observed during sunrise/ sunset and noon. Give explanition of each.

ANSWER NO. 48

Sun appears red at sunrise and sunset. At sunrise and sunset, sun is closer to the horizon. The sunlight passes through denser layer of air and covers longer distance before reaching our eyes. Most of the blue light gets scattered. The light that reaches to us is red.
     That's why the sun appears red at sunrise.
    At noon, the sun is overhead. The sunlight passes through rares layers of air and covers shorter distance before reaching our eye. So, at all colours of light are scattered equally. Hence the sun appears white.

QUESTION NO. 49

Write the various eye defect in human and write how it can be corrected.

ANSWER NO. 49

1. MYOPIA

  Myopia is also known as near - sightedness. A person with myopia can see nearby objects clearly, but cannot see distance object clearly.
        This defect can be corrected by using a concave lens of suitable power.

2. HYPERMETROPIA

   Hypermetropia is also known as far - sightedness. A person with hypermetropia can see distance object clearly but cannot see nearby object clearly.
    This defect can be corrected by using convex lens of appropriate power.

3. PRESBYOPIA

   The power of accommodation of the eye usually decrease with ageing. They find it difficult to see nearby objects comfortably and distance object without corrective eye glasses.
     Such people often requires bi - focal lenses.

CLASS - 10 SCIENCE IMPORTANT QUESTIONS OF MARK 3   FOR BOARD EXAMINATION

QUESTION NO. 40

Law of reflection of light. Define absolute refractive index and Express it mathematically.

ANSWER NO. 40

LAW OF REFLECTION 

1. The angle of incidence is equal to the angle of reflection.
2. The incident Ray, the normal to the mirror at the point of incidence and the reflected ray, all lie in the same plane.

REFRACTIVE INDEX

Refractive index is a number which measures the bending of light when passing from one medium to another. It is the ratio of velocity of light in vacuum to the velocity of light in the medium.

Refractive index = velocity of light in vacuum

                                     velocity of light in medium

QUESTION NO. 41

Define the following and show in the diagram.

1. Centre of curvature
2. Pole
3. Radius of curvature of the mirror
4. Principal axis

ANSWER NO. 41

1.  CENTRE OF CURVATURE  --  The reflecting surface of a spherical mirror form a part of sphere. This point is called centre of curvature.
2. POLE --  The centre of the reflecting surface of a spherical mirror is a point called pole.                        
3.  RADIUS OF CURVATURE OF THE MIRROR   - The radius of the sphere of which reflecting surface of a spherical mirror form a part, is called the radius of curvature.
4.  PRINCIPLE AXIS - It is a straight line passing through the pole and the centre of curvature of spherical mirror.    

       

QUESTION NO. 42

What is law of reflection of light ?

ANSWER NO. 42

LAW OF REFRACTION OF LIGHT

1. The incident ray, the reflected ray and the normal to the interface of two transparent media at the point of incidence, all lie in same plane.
2. The ratio of sign of angle of incident to the Sine of angle of reflection is a constant, for the light of a given colour and for the given pair of media. This law is also known as snell's law of reflection.

 If (i) is the angle of incident (r) is the angle of reflection then,

          Sine i   = Constant

           Sine r

  This constant value is called the reflective index of the second medium with respect to the first.

QUESTION NO. 43

define the following

1. Centre of curvature
2. Principle Axis
3. Optical centre
4. Aperture

ANSWER NO. 43

1. CENTRE OF CURVATURE

     A lens, either a convex lens or a concave lens, has two spherical surface. Each of these surface forms a part of sphere. The centre of this sphere are called centre of curvature of the lens. Represented by letter C.

2. PRINCIPLE  AXIS

  An imaginary straight line passing through two two centres of curvature of a lens is called its principle axis.

3. OPTICAL CENTRE

 The point of a lens is its optical centre. It is usually represented by the letter O.

4. APERTURE 

  The effective diameter of the circular outline of a spherical lens s called its aperture.

QUESTION NO. 44

Why is the colour of the sky  is blue.

ANSWER NO. 44

the molecules of the air and other fine particles in the atmosphere have size smaller than the wave length of the visible light. These are more effective in scattering light of shorter wavelength at the red end.

     The red light has a wavelength about 1.8 times greater than blue light. Thus, When sunlight passes through the atmosphere, the fine particles in air scatter the blue colour more strongly than red. The scattered blue light enters in our eyes. 

CLASS - 10 SCIENCE IMPORTANT QUESTIONS OF MARK 3  FOR BOARD EXAMINATION

QUESTION NO. 50

Define the term power of accommodation. Write the modification in the curvature of the eye lens which enables us to see the nearby object clearly.

ANSWER NO. 59

POWER OF ACCOMMODATION

The ability of eye lens to adjust it's focal lenght is called accommodation. 

     The eye lens lens is composed of a fibrous, jelly - like material. It's curvature be modified to some extent by the ciliary muscles. When we look at objects closer to the eye, the ciliary muscles contract. This increases the curvature of the eye lens. The eye lens then becomes thicker. The focal length of the eye lens decreases. This enable us to see nearby object clearly.

QUESTION NO. 51

When do we consider a student sitting in the class to be myopic ? List two causes of this defect. Explain using a ray diagram how this defect of eye can be corrected.

ANSWER NO. 51

In myopic condition student will not be able to see the written words on the blackboard clearly from the last bench.

 CAUSES

This defect may be arise due to 
(i) Excessive curvature of the eye lens
(ii) Elongation of the eyeball.
    This defect can be corrected by using a concave lens of suitable power.

QUESTION NO. 52

What is scattering of light ? Use this phenomenon to explain why.
(i) the sun appears reddish at sunrise

ANSWER NO. 52

SCATTERING OF LIGHT

Scattering occurs when light pass through an imperfect medium and are deflected from a straight path.

(i) In the morning, the sun is at the horizon sunlight has to travel a long distance through thick layers of air. The colloidal particles in the sky like molecules of air scatter away colours of shorter wavelength like blue. So colours of longer wavelength enter our eye like red. Hence the sun appears reddish during morning.

QUESTION NO. 53

What is rainbow ? Draw a labelled diagram to show the formation of a rainbow.

ANSWER NO. 53

rainbow is an arch of colours visible in the sky, caused by the refracted and dispersion of the sun's light by rain or other water droplets in the atmosphere.

QUESTION NO. 54

Draw magnetic field lines around a bar magnet. List the properties of magnetic field lines. Why two field lines are not crossed each other.

ANSWER NO. 54

PROPERTIES OF MAGNETIC FIELD LINES

1. They do not intersect each other.
2. The force of attraction is strongest near the pole due to more numbers of magnetic field line per unit area at poles.
3. Emerging from the north pole of the magnet to its south pole.

   Two magnetic field lines do not intersect each other because if it happens it means at the point of intersect the the compass needle will show two different direction which is not possible.

CLASS - 10 SCIENCE IMPORTANT QUESTIONS OF MARK 5   FOR BOARD EXAMINATION

QUESTION NO. 11

1. Isomers define.

2. Draw two possible isomers of the compound with molecular formula C3 H6O and write their names.

3. Differentiate East verification and saponification on the basis of chemical equation.

ANSWER NO. 11

1. ISOMERS : 

the compound which have identical molecular formula but different structure are called isomers.
2.

3. ESTERIFICATION REACTION :

  Ester are most commonly formed by reaction of an acid and alcohol. Ethanoic acid reacts with absolute ethanol in the presence of an acid catalyst give and ester.

SAPONIFICATION : 

On heating with Sodium Hydroxide, which is an alkali, the step is converted back to alcohol and sodium salt of carboxylic acid. This reaction is known as saponification.

QUESTION NO. 12

What is methane ? Draw it electron dot structure name the type types of bonds formed in this compound fullstop why are such compounds.

(i) poor conductor of electricity question mark

(ii) have low melting and boiling points? What happen when this compound is burnt in oxygen ?

ANSWER NO. 12

METHANE

It is a compound of carbon. Methane is widely used as a fuel and is a measure component of biogas and compressed natural gas.

Carbon compounds which contain only carbon and hydrogen are called hydrogen carbon. Among these, the saturated hydrogen hydrocarbons are called alkanes. The unsaturated hydrocarbon which contains one or more double Ponds are called alkenes. Those containing one or more triple bonds are called alkynes.

(i) since the electrons are shared between atoms and low charged particle are formed such covalent compounds are generally poor conductor of electricity.

(ii) covalently bonded molecules are strong bonds within the molecules, but intermolecular forces are weak. This gives rise to the low melting and boiling point.

Saturated hydrocarbons generally give a clean flame.

CLASS - 10 SCIENCE IMPORTANT QUESTIONS OF MARK 5 FOR BOARD EXAMINATION

QUESTION NO. 3

The modern periodic table has been evolved through the early attempts of Dobereiner, Newland and Mendeleev.

(a) List one advantage and one limitation of al the three attempts.

(b) Name the scientist who first of all showed that atomic number of an element is a more fundamental property than its atomic mass.

(c) State modern periodic law.

ANSWER NO. 3

(a) ADVANTAGE OF DOBEREINER -

   Chemists look at elements in terms of groups of elements with similar chemical chemical and physical property. 
 DISADVANTAGE 
 All the known elements could not be arranged in the form of triad.

 ADVANTAGE OF NEWLAND 

Newland law of octaves was the first logically bases on the atomic weight.

DISADVANTAGE

New land could arrange element only upto calcium, out of the total 56 elements known.

ADVANTAGE OF MENDELLEV

Arrange the 63 known elements in increasing order of their atomic masses.
DISADVANTAGE
Anomalous pair : Argon with atomic mass 39. 9 precedes potassium with atomic mass 39.1.

(b) Henry Moseley

(c) MODERN PERIODIC LAW :

1. The modern periodic table has 18 vertical columns known as groups and horizontal row known as periods.
2. The Modern Periodic Table is used to organise all the known elements. elements are arranged in the table by increasing atomic number.
3. In the modern periodic table, each element is represented by its chemical symbol. The number above each symbol is its atomic number. Atomic number increases from left to right and from top to bottom in table.
4. All elements can be classified in one of the three classes metal, metalloids or non metals. Elements in each case share certain basic properties.

QUESTION NO. 4

(a) state the reason why carbon cannot form C4+ cation  C4- anions, but form covalent bond. Also state the reason to explain why covalent compounds.

(i) are bad conductor of electricity.

(ii) have low melting and boiling points.

(b) write the structural formula of benzene C6H6

ANSWER NO. 4

Carbon has four electrons in its outermost shell and need to gain or lose 4 electrons to attend noble gas configuration.

• It could gain four electrons forming C4 - and anion, but it would be difficult for the nucleus with 6 protons to hold on 10 electrons that is 4 extra electrons.
•  It could lose four electrons forming C4+ cation. But it would required a large amount of energy to remove 4 electrons leaving behind carbon 6 protons in it's nucleus holding on just two electrons.

         Carbon overcome this problem by sharing is Valence Electrons with other atoms of carbon or with atoms of other elements and form a covalent bond.

(i) since in covalent bond the electrons are shared between atoms and low charged particle are formed, such covalent compound are generally poor conductor of electricity.

(ii) covalently bonded molecules are seen to have strong bonds with the molecules, but intermolecular force are the full stop this give life is too low melting and boiling points of these compound.

(b) Structural formula of benzene.

CLASS - 10 SCIENCE IMPORTANT QUESTIONS OF MARK 3   FOR BOARD EXAMINATION

QUESTION NO. 6

Why is respiration considered an exothermic reaction ? Explain.

ANSWER NO. 6

During digestion, food is broken down into simpler substance. Carbohydrates are broken down to form glucose. This glucose combines with oxygen in the cell of our body and provides energy. The special name of this reaction is respiration.

QUESTION NO. 7

Write the importance of PH in everyday life.

ANSWER NO. 7

1. Our digestive system - Hydrochloric acid produced in our stomach helps the digestion of food. But when the amount of acid goes beyond a certain limit you to  indigestion, pain and irritation are created. To neutralize if that of excess acid magnesium Hydroxide (milk of magnesia) is a my base used as antacid.

2. Acid cause tooth decay : Tooth decay starts when the pH of mouth is lower than 5.5. The best way to prevent this clean the mouth after eating.

3. To determine the pH value of river, because living organism can survive in a narrow range of PH change.

4. Plants required a specific pH range for their healthy growth.

5. Animals used acid for their protection which causes pain and irritation use of mild base light baking soda on stung part given relief.

QUESTION NO. 8

Write the chemical equation to produce the bleaching powder and write its uses.

ANSWER NO. 8

The chlorine gas is used for the manufacture for men of bleaching powder. Bleaching powder is produced by the action of chlorine on dry slaked lime. (Ca(OH)2).
      Ca(OH)2 + Cl2 -------------> CaOCl2+H2O

USES OF BLEACHING POWDER :
1. Bleaching cotton and lining in the textile industry, paper industry and it is also used in laundry.

2. In many chemical industry it is used as oxidizing agent.

3. It act as antigerm for drinking water.

QUESTION NO. 9

A white powder is added while baking cakes to make it soft and spongy. Name main ingredients.  Explain the function of each ingredient. Write the chemical reaction taking place when the Powder is heated during baking.

ANSWER NO. 9

Name of compound is sodium hydrogen carbonate (NaHCO3).
       The common name is baking soda. It is commonly used in kitchen for making tasty crispy pakoras.

  2NaHCO3 -----------------------> Na2CO3 + H2O + CO2

1. Carbon dioxide produced during their reaction can cause bread or cake to rise making them soft and spongy.
2. Sodium hydrogen carbonate is also an ingredient in antacid. Being alkaline, it neutralize excess of in stomach and provide relief.
3. It is also used in Soda acid fire extinguisher.

QUESTION NO. 10

With a labelled diagram describe in brief an activity to show the formation of an Easter.

ANSWER NO. 10

1. Take one ml ethanol (absolute alcohol) and 1 ml glacial Acetic Acid along with few drops of concentrated sulphuric acid in a test tube.
2. Warm this mixture in water but for at least five minutes.
3. Pour into a beaker containing 20 to 50 ml of water and smell the result mixture. This is the formation of Easter.

ALSO SEE IMPORTANT QUESTIONS OF 3 MARK

From question no. 1 to 5

CLASS - 10 SCIENCE IMPORTANT QUESTIONS OF MARK 5 FOR BOARD EXAMINATION   

QUESTION NO. 5

(a) How is valency of element determined if its electronic configuration is known ? Determine the valency of an element of atomic no.9 .
(b) Given below are some elements of the modern periodic table. Atomic number of the elements are given in parenthesis:
    A(4), B(9), C(14), D(19), E(20)

(i) With the help of electronic configuration, find out which one of the above element will have one electron in its outermost shell.
(ii) Which two elements belongs to the same group ? Give reasons for your aswe.
(iii) Which one of the above element belonging to the fourth period has bigger atomic radius and why ?

ANSWER NO.5

(a) An elements valency is determined by the number of electrons in its outer shell. Hence, the number of valence electrons obtained from the electronic configuration of the element gives the valency i.e. the number of electrons lost, gained or shared by the element to attain the noble gas configuration.

(b)  (i)  A(4)  =  2,2
              B(9)  =  2,7
              C(14)  =  2,8,4
              D(19)  =  2,8,8,1
              E(20)  =  2,8,8,2
Element D will have one electron in its outer shell.
(ii) Element A and E will belong to the same group because according to the modern periodic table the elements present in any one group have the same number of valence electron. Periodic table signify an identical outer shell electronic configuration.
(iii) Element D belongs to the fourth period. Element D has a greater atomic radius,because according to the modern periodic table when move down a group, the atomic radius increase and when move from left to right in a period the atomic radius decreases.

QUESTION NO. 6

(a) What is double displacement reaction ? Explain with an example.
(b) A small amount of quicklime is added to water in a beaker.
(i) Name and define the type of reaction that has taken place.
(ii) Write balanced chemical equation for the reaction for the above reaction and the chemical name of the product formed.
(iii) List two main observations s reaction.

ANSWER NO. 6

(a) DOUBLE DISPLACEMENT REACTION :

The reaction in which an exchange of ions between the reactants are called double displacement rections.
Na2SO4 + BaCl2 ----------->BaSO4 + 2NaCl
(b) It is combination equation.

(i) DEFINITION :

     In this reaction a single product is formed from two or more reactants.
(ii) CaO + H2O ----------->  Ca(OH)2 + Heat

In this reaction, calcium oxide and water combines to form a single product, calcium hydroxide.

(iii) OBSERVATION

1. Calcium oxide reacts vigorously with water to produce slaked lime releasing a large amount of heat.
2. A hissing sound is produced. Precipitate is formed.

CLASS - 10 SCIENCE IMPORTANT QUESTIONS OF MARK 3   FOR BOARD EXAMINATION

QUESTION NO. 16

An ore on treating with dilute hydrochloric acid produce brisk effervescene. Name the type of ore with one example. What step will be required to obtain metal from the enriched ore ? Also write the chemical equation for reaction involved in this process.

ANSWER NO. 16

Type of ore is carbonate ore.

The following steps required to obtain pure metal from this ore.

1. Calcination, to obtain oxide of the metal.

2. Reduction, reacting the oxide of metal with carbon monoxide.

3. As a result pure metal is be obtained.

   ZnCO3 ---------------------> ZnO + CO2

  ZnO + CO --------------->  Zn+ CO2

QUESTION NO. 17

When copper powder is heated in China dish the reddish brown surface of copper powder becomes coated with a black substances.

(a) why has the black substance formed?

(b) what is this black substance ?

(c) write the chemical equation of the reaction that takes place.

(d) how can the black coating on the surface be turned reddish Brown.

ANSWER NO. 17

(a) The black colour substance is formed by the                    reaction of copper with oxygen.

(b) the black colour substance is Cuo copper ii oxide.

(C)  2Cu2 + O -----------------------> 2CuO

(d) The copper oxide does form can be reduced to its         basic metal form by reducing it with hydrogen or         carbon monoxide.

QUESTION NO. 18

When potassium iodide solution is added to a solution of Lead Nitrate in a test tube, a precipitate is formed.

(a) what is the colour of this precipitate full? Name the compound precipitated.

(b) write the balanced chemical equation for this reaction.

(c) list two types of reaction in which this reaction can be placed.

ANSWER NO. 18

(a) the resulting precipitate is lead iodide PbI2 and its bright yellow.

(b) Pb(NO) + 2KI = PbI + 2KNO

(c) 1. Precipitation reaction as a yellow coloured precipitate of lead iodide is formed.

    2. Double displacement reaction.

QUESTION NO. 19

List in tabular form three physical to chemical properties on bases with ethanol and ethanoic acid can be determined.

ETHANOL
CHEMICAL PROPERTY

• No reaction on Litmus Paper
• No reaction with NaHCO3

PHYSICAL PROPERTY

• Low boiling point
• Pleasant smell
• Burning taste

ETHANOIC  ACID
CHEMICAL PROPERTY

• Turns blue Litmus to red
• React with NaHCO3 to give brisk sense of CO2

PHYSICAL PROPERTY

• High boiling point
• Purgent smell

•  Sour taste

QUESTION NO. 20

(a) state two properties of Carbon which lead to a very large number of carbon compound.
(b) why does micelle form formation takes place when soap is added to water? Why micelle do not form when soap is added to ethanol.

ANSWER NO. 20

(a) the two properties of Carbon that give rise to a large number of compounds are as follows -

1. CATENATION :

It is the ability to form bonds with other atoms of carbon.

2. TETRAVALENCY :

With the valency of four, carbon is capable of bonding with four other atoms.

(b) the molecules of soap are sodium or potassium salt of long chain carboxylic acid. The ionic and of soap interacts with water why is the carbon chain interacts with oil. The soap molecules, does form structure called micelles.
          Micelle formation does not take place in ethanol because the alkyle chain of soap becomes soluble in alcohol.

CLASS - 10 SCIENCE IMPORTANT QUESTIONS OF MARK 5   FOR BOARD EXAMINATION

QUESTION NO. 1

What is difference between soap and detergent? State in brief the cleansing action of soap in a movie and always got from a fabric. Why are so are not very effective when fabric is washed in hard water? How is this problem resolved.

ANSWER NO.1

          Soaps are sodium salt of long chain carboxylic acid. Whereas  detergents are sodium salt of long chain benzene sulphonic acid. Detergents are soluble in hard water, whereas so do not work in hard water. Dirts are oily in nature, all does not dissolve in water. The molecules of soap are Sodium and potassium salt of long chain carboxylic acid. The ionic end of soap interact with water while the  carbon chain interact with oil. The soap molecules, thus form structures called micelles where one end of the molecules towards the oil droplet while the ionic end faces  outside. This form and emulsion in water. The soap micelles thus  help in pulling out the dirt in water and clothes are cleaned.
            This is caused by the action of soap with calcium and magnesium salt, which cause the hardness of water. Hence a large amount of water is needed. 
              This problem is overcome by using another class of compound called detergent as a cleaning agent.

QUESTION NO. 2

(a) activity to demonstrate the decomposition reaction of Lead Nitrate.
(b) draw a labelled diagram of experimental setup. List to main observations.
(c) balanced chemical equation for the reaction stating the physical state of reactant and the product.

ANSWER NO. 2 

(a) 1. Take to take about 2 gram Lead Nitrate powder in a boiling tube.
2. Hold the boiling tube and heat over frame.

(b) OBSERVATION 

• When Lead Nitrate is heated it produces a yellow precipitate of lead monoxide.
• It also produces a brownish colour tube which is Nitrogen dioxide along with oxygen. 

(c) 2Pb(NO3)2  ----------------->2PbO + 4NO2 + O2

CLASS - 10 SCIENCE IMPORTANT QUESTIONS OF MARK 1 FOR BOARD EXAMINATION   

QUESTION NO. 101

What are outside raw materials used for an organism?

ANSWER NO. 101

1. WATER : which is used for digestion of food and also useful for certain body function.
2. OXYGEN : oxygen is useful for breakdown of food which provide energy and it is very essential for in organism to live.
3. FOOD : it is obligatory source of energy for a body.

QUESTION NO.102 

What is role of the acid in our stomach?

ANSWER NO. 102

Stomach acid activates the enzyme pepsin needed for protein digestion. Stomach acid signals to the pancreas to produce digestive juices and enzymes to further breakdown of food.

QUESTION NO. 103

What is the function of digestive enzymes?

ANSWER NO. 103

Digestion is set of biochemical reaction. Digestive enzymes are bio catalyst which can increase the rate of biochemical reaction.

QUESTION NO.  104

Write the names of enzyme secreted by

•  Mouth
• Pancreas

ANSWER NO. 104

• Mouth - Amylase
• Pancreas - Amylase, trypsin, lipase.

QUESTION NO. 105

What is stomata?

ANSWER NO. 105

Stomata on small pores present in leaf. They are surrounded by guard cells which help in closing and opening of stomata.

QUESTION NO. 106

What is the function of alveoli?

ANSWER NO. 106

 Through alveoli oxygen is taken into the body and carbon dioxide is eliminated, in this the alveoli gaseous exchange takes place.

QUESTION NO. 107

What is alveoli?

ANSWER NO. 107

It is the pouch like air sac at the end of smallest bronchioles are called alveoli.

QUESTION NO. 108

Write the function of artery and veins.

ANSWER NO. 108

Arteries carry blood from the heart to the rest of the body, whereas veins carry blood from rest of the body back to heart. Almost all arteries carry oxygenated blood and almost all carry deoxygenated blood.

QUESTION NO. 109

What is the function of platelets in blood ?

ANSWER NO.  109

Platelets or blood cell responsible for blood clotting. If a blood vessel wall becomes damage, platelets will rush to the site of injury and form a plug or clot to stop the bleeding.

QUESTION NO. 110

What is lymph, write its function in the body.

ANSWER NO. 110

Lymph is the fluid that circulates throughout the lymphatic system. The primary function of lymphatic system is to transport lymph, a fluid containing infection fighting white blood cells, throughout the body.

ALSO SEE IMPORTANT QUESTION OF 1 MARK

From question no. 31 to 40


From question no. 1 to 10

From question no. 21 to 30

From question no. 41 to 50

From question no. 51 to 60

From question no. 61 to 70

From question no. 71 to 80

From question no. 81 to 90

From question no. 101 to 110

From question no. 111 to 120

From question no. 121 to 130