Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).

**Assertion (A):**

![](https://res.cloudinary.com/ddr1kuyb3/image/upload/v1786117431/questions/k4mtdfljtocfcyzgtnqu.png)

undergoes $S_N2$ reaction faster than

![](https://res.cloudinary.com/ddr1kuyb3/image/upload/v1786117432/questions/iqbaj5mazn4tgivspcic.png)

**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:

Question

Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).

**Assertion (A):**

![](https://res.cloudinary.com/ddr1kuyb3/image/upload/v1786117431/questions/k4mtdfljtocfcyzgtnqu.png)

undergoes $S_N2$ reaction faster than

![](https://res.cloudinary.com/ddr1kuyb3/image/upload/v1786117432/questions/iqbaj5mazn4tgivspcic.png)

**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:

Accepted Answer

C. 1. In an $S_N2$ reaction, the incoming nucleophile attacks the carbon at the same time the leaving group departs, so anything that makes the leaving group leave more easily speeds up the whole reaction.

2. As we go down a halogen family, the atomic size increases, so the carbon–halogen bond gets longer and weaker.

Given this trend,

$$
Bond\ Strength:\ C	ext{-}F > C	ext{-}Cl > C	ext{-}Br > C	ext{-}I
$$

3. Since the $C	ext{-}I$ bond is the weakest, it breaks most easily during the reaction.

4. Also, the iodide ion formed, $I^-$, is very stable because its negative charge is spread over a large volume, so it does not mind leaving the carbon.

5. Because of both the weak $C	ext{-}I$ bond and the stability of $I^-$, the iodo-compound reacts faster in $S_N2$ substitution than the corresponding chloro-compound. This confirms **Assertion (A)** is true.

6. **Reason (R)** correctly explains this by pointing out that iodine's large size stabilises the leaving $I^-$ ion, which is exactly why (A) happens.

Hence, both (A) and (R) are true and (R) correctly explains (A), so the answer is **option C**.