(i) A + B → C

The above reaction occurs because the stability of C is higher than the stability of A and B. Molecules always tend to attain the most stable configuration in a reaction.

Here saturated compounds are more stable than unsaturated compounds. The double/triple bonds present in the unsaturated compound break to form single bonds by combining with the reactant to attain a highly stable product. Therefore, unsaturated hydrocarbons show addition reaction.

(ii) Alcohol supplied for industrial purpose is mixed with chemicals like methanol to prevent the misuse of it. It is a common practice to overuse this alcohol for recreational purposes, and addition of these chemicals would help prevent the misuse to an extent. To identify such mixtures of alcohols, dyes or coloured substances are added to colour the alcohol blue. In this case, the coloured substance added is copper sulphate.