Question: 84. Given below are two statement: one is labelled as Assertion (A) and the other is labelled as Reason (R):
Assertion (A): 
undergoes \mathrm{S}_{\mathrm{N}} 2 reaction faster than 
Reason (R): Iodine is a better leaving group because of its large size.
In the light of the above statements, choose the correct answer from the options given below:
(1) Both \mathbf{A} and \mathbf{R} are true and \mathbf{R} is the correct explanation of \mathbf{A}.
(2) Both \mathbf{A} and \mathbf{R} are true but \mathbf{R} is not the correct explanation of \mathbf{A}.
(3) \mathbf{A} is true but \mathbf{R} is false.
(4) \mathbf{A} is false but \mathbf{R} is true.
Answer: Option (1)
Explanation:
In an \mathrm{S}_{\mathrm{N}} 2 reaction,
the rate depends on the nature of the leaving group.
A better leaving group increases the rate of nucleophilic substitution.
Iodine has a larger atomic size compared to chlorine,
which results in a longer and weaker carbon–iodine bond.
Due to its large size, iodide ion can better stabilize the negative charge after leaving,
making it a better leaving group.
Therefore, undergoes \mathrm{S}_{\mathrm{N}} 2 reaction faster than
Thus, Assertion (A) is true.
The reason correctly explains why iodine is a better leaving group and hence explains the assertion.
Therefore, both Assertion (A) and Reason (R) are true,
and Reason (R) is the correct explanation of Assertion (A).