Assertion (A): $\text{ICl}$ is more reactive than ${\text{I}}_2$.Reason (R): $\text{I-Cl}$ bond is weaker than $\text{I-I}$ bond.

Interhalogen compounds ($\text{X-X’}$) are generally more reactive than pure halogens (except ${\text{F}}_2$).Assertion is correct: $\text{ICl}$ reacts faster than ${\text{I}}_2$.Reason is correct: The bond between two different halogens is more polar and weaker than the bond in a pure diatomic halogen (due to less effective overlap).Since the higher reactivity of $\text{ICl}$ is a direct consequence of the weaker $\text{I-Cl}$ bond, (R) explains (A).