Given below are two statements, one is labelled as Assertion A and the other is labelled as Reason R.
Assertion A : Isotopes of hydrogen have almost same chemical properties, but difference in their rates of reactions.
Reason R: Isotopes of hydrogen have different enthalpy of bond dissociation.
In the light of the above statements, choose the most appropriate answer from the options given below:

Assertion A: Isotopes of hydrogen (H, D, T) have almost the same chemical properties because they have the same electronic configuration. However, their rates of reactions differ due to the kinetic isotope effect (heavier isotopes react slower). This is correct.

Reason R: Isotopes of hydrogen have different bond dissociation enthalpies. The H-H bond has a lower dissociation energy than D-D bond because of the difference in zero-point energies (heavier isotopes have lower zero-point energy, making their bonds slightly stronger). This is correct.

The difference in bond dissociation enthalpy directly causes the difference in reaction rates (kinetic isotope effect), so R correctly explains A.

Both A and R are correct and R is the correct explanation of A.

This matches option 2.