Answer
(b) $\mathrm{W.s}$ is not a unit of power.
Work Step by Step
We have, power
\begin{align*}
P=\frac{E}{t}
\end{align*}where energy, $E$ has the unit of $\mathrm{J}$. Thus, the unit of power is $\mathrm{J/s}$; also called $\mathrm{Watt \,(W)}$ or $\mathrm{horsepower (hp)}$.
$\mathrm{W.s}$ is not a unit of power.
