In the equations given below, state giving reasons, whether substances have been oxidised or reduced.
(i)  PbO + CO  →Pb + CO₂ (ii) H₂S + Cl₂ →2HCl + S.

1 What is the method of balancing chemical equation? 2 Why is it necessary to balance a chemical equation? 4 A sample of water weed was placed in water and exposed to sunlight. Bubbles of a gas are seen on the surface of the leaves.
(i) Name the gas evolved.
(ii) Name the process taking place.
(iii) Write a balanced equation of reaction taking place. 5 Give balanced equations, wherever possible, or where this is not possible, explain the following by means of examples:
(i) A reaction which gives out heat.
(ii) A reaction which takes place with the help of sunlight.
(iii) A reaction which is brought about by electric current.
(iv) Reversible Reactions.
(v) A reaction with a solid and gas which produces heat.