Chemistry · Alkyl Halides and Amines

The correct answer is option (C): Two-step mechanism.

The SN1 mechanism, also known as the substitution nucleophilic unimolecular mechanism, is a two-step mechanism.

This statement is incorrect. In the SN1 mechanism, the formation of the carbocation intermediate is the slow step. 

This statement is incorrect. The SN1 mechanism is not a single-step mechanism. It is a two-step process: the formation of a carbocation intermediate in the first step and the attack of a nucleophile on the carbocation in the second step.

This statement is correct. The SN1 mechanism is a two-step mechanism. In the first step, the leaving group departs from the substrate, resulting in the formation of a carbocation intermediate. In the second step, a nucleophile attacks the carbocation, leading to the substitution of the leaving group with the nucleophile.

This statement is partially correct. In the SN1 mechanism, the attack of the nucleophile on the carbocation is indeed a slow step. Carbocations are unstable intermediates and form quickly, but their reactivity is relatively low. As a result, the rate-determining step is usually the nucleophilic attack on the carbocation, which is a slower process.

This statement is also partially correct. Primary alkyl halides are more likely to undergo SN2 (Substitution Nucleophilic Bimolecular) reactions rather than SN1 reactions. In SN2 reactions, the nucleophile directly displaces the leaving group in a single concerted step. Primary alkyl halides are more favorable for SN2 reactions because they have less steric hindrance, which allows the nucleophile to attack from the backside of the carbon more easily. SN1 reactions are more commonly observed with tertiary alkyl halides where the carbocation can be stabilized by neighboring alkyl groups.