-

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.






Comments

Post a Comment

Popular posts from this blog

-
ENGLISH CLASS - 6  CHAPTER - 8 A GAME OF CH ANCE    WORKING WITH THE TEXT QUESTION A Complete the following sentences from memory choosing a phrase from those given in brackets. 1. --------------------------was held at the time of Eid festival.( A big show, A big fair, A big competition) 2. Tradesmen came to the village with all  kinds of goods ----------. (to display, to buy, to sell) 3. Uncle told me -------------- while  he was away.(not to buy anything, not to go anywhere, not to talk to anyone) 4. The owner of the Lucky Shop wanted everybody present ------------------------- .  (to play the game, to win a prize, to try their luck) 5. The first time I took a chance I got --------------.(a bottle of ink, two pencils, a trifle) 6. Uncle told me that the shopkeeper had made --------------.(a fool of me, a good profit, friends with many people) ANSWER 1. A big fair 2. to sell 3. not to buy anything 4. to try their luck 5. two...
Read more
-
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) + CO2 2 (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. Fe 2 O 3 + 2Al → Al 2 O 3 + 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...
Read more

FULL FORM OF NSCCL

-
     NSCCL stand for National Securities Clearing Corporation of India Limited.Now it is known as NSE clearing limited. It is a wholly owned subsidiary of NSE which is responsible for clearing and settlement of all trades executed on NSE and deposit and collateral management and risk management function.It was the first clearing corporation to be established in India and introduced as settlement guarantee before it became a regulatory requirement. OBJECTIVE OF NSCCL There are some objectives of the NSCCL which are as follows- 1. To bring and sustain confidence in clearing and settlement of securities. 2. Promoting and maintaining short and consistent settlement cycles. 3. Provides counter party risk guarantee. 4. To operate a tight risk containment system.      As per CRISIL,the rating reflects NSCCL's status as Clearing Corporation for NSE. The rating also factors in NSCCL's rigorous risk management controls and adequate settlement guarant...
Read more