CrO Basic oxide
$\mathrm{Cr}_2 \mathrm{O}_3$ Amphoteric oxide
In $\mathrm{CrO}, \mathrm{Cr}$ exist as $\mathrm{Cr}^{+2}$ and have $\mu$ only $=4.90$
In $\mathrm{Cr}_2 \mathrm{O}_3, \mathrm{Cr}$ exist as $\mathrm{Cr}^{+3}$ and have $\mu$ only $=3.87$
Sum of spin only magnetic moment
$ \begin{aligned} & =4.90+3.87=8.77 \\
& \mu_{\text {only }}=877 \times 10^{-2}
\end{aligned} $

Ans. 877