Name the gas evolved when potassium nitrate crystals are heated with concentrated sulphuric acid.

What happens when nitric acid is added to an egg shell?

Which gas is evolved when hydrochloric acid is added in first test tube containing small pieces of marble and then in second test tube containing zinc granules?

What happens when an acid or a base is added to the water? Why does the beaker appear warm? Why should we always add acid or base to the water and not water to the acid or base?

Give reasons:

(i) Use of a mild base like baking soda provides relief on the area stung by honeybee.

(ii) Baking powder is added to make the cakes spongy and soft.

(iii) The colour of blue copper sulphate crystals changes to white on heating.