# Given below are two statements :

Question:

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

Assertion (A) : Heavy water is used for the study of reaction mechanism.

Reason (R) : The rate of reaction for the cleavage of $\mathrm{O}-\mathrm{H}$ bond is slower than that of $\mathrm{O}-\mathrm{D}$ bond. Choose the most appropriate answer from the options given below :

1. Both (A) and (R) are true but (R) is not the true explanation of (A).

2. Both $\mathbf{( A )}$ and $\mathbf{( R )}$ are true and $\mathbf{( R )}$ is the true explanation of (A).

3. (A) is false but $\mathbf{( R )}$ is true.

4. (A) is true but $(\mathbf{R})$ is false.

Correct Option: , 4

Solution:

$\mathrm{D}_{2} \mathrm{O}$ in used for the study of reaction mechanism. Rate of reaction for the cleavage of $\mathrm{O}-\mathrm{H}$ bond $>$ O-D bond.