(a) Give an example for a combination reaction which is exothermic.
(b) Identify the oxidising agent and reducing agent in the following reaction.
`H_(2)S + Cl_(2) to 2HCl + S`
(c) Name the phenomenon due to which the taste and smell of oily food changes when kept for a long time in open. Suggest one method to prevent it.

Explanation

(a) `CaO + H_(2)O to Ca (OH)_(2) + "heat"`.
(b) `H_(2)S + Cl_(2) to 2HCl + S`
Oxidising agent `Cl_(2)` , Reducing agent `H_(2)S`.
(c) It is known as rancidity. Only food must be kept in air tight containers.