The mechanism of S N 1 reaction is given as : R-X → R⊕ X⊖ → R⊕ ∥ X⊖ →(Y⊖) R-Y + X⊖
A student writes general characteristics based on the given mechanism as :
(a) The reaction is favoured by weak nucleophiles.
(b) R⁺ would be easily formed if the substituents are bulky.
(c) The reaction is accompanied by racemization.
(d) The reaction is favoured by non-polar solvents.

Solution

Chemistry ma’am · 2 steps

Read the mechanism: a bare carbocation forms first, so ask what helps it form and what happens to it next.

1. Slow step. In S_N1 the slow step is R-X breaking into R⁺ and X⁻. The nucleophile Y⁻ joins only after that, so it plays no part in the rate.

   Statement	What the mechanism says	Verdict
   (a) Weak nucleophiles favour it	Y⁻ is not in the slow step. A weak nucleophile does not slow S_N1, but it does slow the competing S_N2.	True
   (b) Bulky groups help R⁺ form	Bulky alkyl groups push electrons into R⁺ and are crowded less once the carbon turns planar (sp²), so ionisation is easier.	True
   (c) Racemization occurs	R⁺ is planar, so Y⁻ can attack from either face and both enantiomers form.	True
   (d) Non-polar solvents favour it	The ion pair and the solvent-separated ion pair need a polar (protic) solvent to stabilise the ions.	False

2. So. Statements (a), (b) and (c) are correct and (d) is wrong, which is option (b).

The idea to keep. For S_N1, think carbocation: stable R⁺ (bulky, tertiary), polar protic solvent, nucleophile strength irrelevant, and a planar ion that gives racemization.

Answer from the NTA final answer key. Solution by PrepWiser.