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


QUESTION NO. 1

Define Rancidity. How it can be prevented ?

ANSWER NO. 1

When fat or oil containing food exposed to air, light or moisture it oxidised and become rancid, their smell and taste change. This is called rancidity.
PREVENTION
1. Substances which prevents oxidation are added to food containing fats and oil.
2. Keeping food in air tight containers helps to slow down oxidation.
3. Nitrogen gas is flushed bags of chips to prevent getting oxidised.

QUESTION NO. 2

Define corrosion. How it can be prevented.

ANSWER NO. 2

Corrosion is a natural process that convert a refined metal into a more chemically stable form such as oxide, hydroxide, or sulfide. It is the gradual destruction of material by chemical reaction with environment.
PREVENTION
1. Galvanisation of metals.
2. Alloying of metals when iron is mixed with nickel and chromium, stainless steel form which is rust free.
3. Avoid metals to expose in moisture.
4. Application of corrosion inhibitor such as primer and then paint.

QUESTION NO. 3

2 gm of ferrous sulphate crystals are heated in a big dry boiling tube.
(a) List any two observations.
(b) Name the types of chemical reaction taking place.
(c) Write balanced chemical reaction taking place.

ANSWER NO. 3

(a)1. The gas emitted has the characteristic odour of burning sulphur.
     2.On heating, the colour changes from light green to white.
(b)this reaction is called decomposition reaction.
(c) 2FeSO4 ------------> Fe2O3+SO2+SO3

QUESTION NO. 4

Name the ore of mercury. Write the help of balanced chemical equation, explain the process of extraction of mercury from its ore.

ANSWER NO. 4

Cinnabar is an ore of mercury. The oxide of mercury can be reduced to metals by heating alone when ore of mercury is heating in air, it convert to mercuric oxide. Mercuric oxide is then reduced to further heating.
                   2HgS+3O2-------->2HgO+2SO2
                    2HgO-------> 2Hg+O2

QUESTION NO. 5

What is amphoteric oxides ? Give two examples of amphoteric oxides.

ANSWER NO. 5

Oxides of metals which have acidic as well as basic behaviour are known as amphoteric oxides. Such metallic oxides reacts with acid as well as base to produce salt and water. Examples of amphoteric oxides are aluminium oxide and zinc oxide.

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