Give the mechanism of substitution nucleophilic unimolecular, `S_N1` reactions.

Give the mechanism of substitution nucleophilic bimolecular, S_N^2 reactions.

Differentiate between (Substitution nucleophilic unimolecular reaction) and (Substitution nucleophilic bimolecular reaction) reactions.

Give the mechanism of sulphonatin of benzene.

Give the mechanism of chlorination of methane.

what is substitution reaction?