(a) List two observations that are noticed when an iron nail is put inside copper sulphate solution. Write chemical equation for the reaction that occurs.
(b) Explain two ways by which rancidity of food materials can be checked.

Explanation

(a) (i) Blue colour of copper sulphate solution changes to light green which is almost colourless.
(ii) A brown mass gets deposited around the nail. For details, consult section 1.5.
(b) (i) Food materials must be kept in air tight bottles.
(ii) In bags containing food materials such as potato chips and other food stuff, air must be replaced by nitrogen.