A : Equivalent weight of $Cu$ in $CuO$ is $63.6$ and in ${Cu}_{2}O$ is $31.8$.

R : Equivalent weight of an element $=\frac{\text{ Atomic weight of an element }}{\text{ Valency of the element }}$

In $CuO$,

Equivalent weight of $Cu=63.6/2=31.8$

In ${Cu}_{2}O$

Equivalent weight of $Cu=63.6/1=63.6$

Thus, the assertion is incorrect and the reason is correct. Hence, option (D) is correct.