If the refractive index of glass with respect to air is $3/2$, what is the refractive index of air with respect to glass?

The correct option is D $\frac{2}{3}$
$a{\mu }_g=\frac{{\mu }_g}{{\mu }_a}=\frac{3}{2}$
where,
$a{\mu }_g=$ Refractive index of glass w.r.t. air
${\mu }_g=$ Refractive index of glass
${\mu }_a=$ Refractive index of air
Thus,
$g{\mu }_a=\frac{{\mu }_a}{{\mu }_g}=\frac{2}{3}$
where,
$g{\mu }_a=$ Refractive index of air w.r.t. glass