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

Give the mechanism of substitution nucleophilic unimolecular, S_N1 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?