Final answer:
Acylation of amines tends to produce monosubstituted products due to the steric hindrance from the acyl group. Alkylation can lead to polysubstitution because the intermediate is more nucleophilic and prone to further reaction. Therefore, both assertion and reason are correct, making the answer D.
Step-by-step explanation:
The question is concerned with the difference in products obtained when amines undergo acylation versus alkylation. The assertion being examined is that acylation of amines yields a monosubstituted product, whereas alkylation leads to a polysubstituted product. The reason given is that an acyl group hinders the approach of further acyl groups due to steric hindrance.
When considering the reactivity of amines with acylating agents, such as acid chlorides or anhydrides, the resultant product is typically an amide. This substitution reaction is generally less prone to further reaction due to the bulkiness of the acyl group, which indeed provides steric hindrance that discourages additional acylation.
Contrastingly, when amines are alkylated, often using alkyl halides, the initial product is a more nucleophilic species which can undergo further alkylation. This leads to the potential for overalkylation, hence yielding polysubstituted products unless steps are taken to prevent this.
With the provided explanation, we can see that the statement of assertion and the reason are both correct, and the reason does correctly explain the assertion.