Question

Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A): I$^-$ undergoes SN$_2$ reaction faster than Cl$^-$.
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:

• A. Both A and R are true but R is not the correct explanation of A.
• B. A is true but R is false.
• C. A is false but R is true.
• D. Both A and R are true and R is the correct explanation of A.

Hint:

In SN\(_2\) reactions, the leaving group ability increases with the size of the atom, as larger atoms can stabilize the negative charge better after departure. This is why I\(^-\) is a better leaving group than Cl\(^-\).

Answer 1

The Correct Option is D

- Assertion (A): It is true that I\(^-\) undergoes SN\(_2\) reactions faster than Cl\(^-\). This is because I\(^-\) is a larger ion with a more diffuse electron cloud compared to Cl\(^-\), making it a better nucleophile and more willing to leave in an SN\(_2\) mechanism.
- Reason (R): Iodine is indeed a better leaving group than chlorine due to its larger size and better ability to stabilize the negative charge once it departs from the carbon atom. The larger atomic size allows iodine to better accommodate the electron density, which is why it is a better leaving group.
Thus, both the assertion and the reason are true, and the reason correctly explains the assertion.
Therefore, the correct answer is (4) Both A and R are true and R is the correct explanation of A.