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 O - H bond is slower than that of O - D bond.

Choose the most appropriate answer from the options given below :

1. A Both (A) and (R) are true but (R) is not the true explanation of (A).
2. B Both (A) and (R) are true and (R) is the true explanation of (A).
3. C (A) is false but (R) is true.
4. D (A) is true but (R) is false. Correct answer