Assertion (A): Zr and Hf are of almost similar atomic radii.

Reason (R): This is due to lanthanoid contraction.

Assertion (A): The units of rate constant of a zero order reaction and rate of reaction are the same.

Reason (R): In zero order reaction, the rate of reaction is independent of the concentration of reactants.

Assertion (A): Inversion of configuration is observed in $\mathrm{S}_{\mathrm{N}} 2$ reaction.

Reason (R): The reaction proceeds with the formation of carbocation.

Assertion (A): p-methoxyphenol is a stronger acid than $p$-nitrophenol.

Reason (R): Methoxy group shows + I effect whereas nitro group shows -I effect.