Magnetic moment of revolving electron,
${\mu }_e=i\times A$
where, $i$ = current and A = area,
${\mu }_e=\frac{e}{T}\times \pi r^2$ (As current, $i=\frac{current}{time}=\frac{e}{t}$ )
where, T = time period of revolution and r = radius of orbit.

${\mu }_e=\frac{e}{2\pi r}\times v\times \pi r^2$
$\left(\because Timeperiod\left(T\right)=\frac{dis\mathrm{t}\mathrm{a}\mathrm{n}ce}{speed}\right)$
where, v = velocity of revolving electron
$\Rightarrow {\mu }_e=\frac{evr}{2}$
Hence, the magnetic moment of revolving electron is $\frac{evr}{2}$