Refractive index of diamond with respect to glass is 1.6 and the absolute refractive index of glass is 1.5. Find out the absolute refractive index of diamonds. 

Glass's absolute refractive index may be readily determined by applying the formula, ${\mu }_{dg}=\frac{{\mu }_d}{{\mu }_g}$, here ${\mu }_{dg}$ is the difference between the refractive indices of glass and diamond, ${\mu }_d,{\mu }_g$ are the glass and diamonds' respective absolute refractive indices.
Formula used $-{\mu }_{dg}=\frac{{\mu }_d}{{\mu }_g}$.

Diamond's refractive index in relation to glass ${\mathrm{n}}_{\mathrm{dg}}=1.6$
Glass's index of refraction ${\mathrm{n}}_{\mathrm{g}}=1.5$
the diamond's refractive index ${\mathrm{n}}_{\mathrm{d}}=$ ?
Diamond's refractive indices with respect to glass ${\mathrm{n}}_{\mathrm{dg}}=\frac{{\mathrm{n}}_{\mathrm{d}}}{{\mathrm{n}}_{\mathrm{g}}}$
hence, the diamond's refractive index ${\mathrm{n}}_{\mathrm{d}}={\mathrm{n}}_{\mathrm{dg}}\times {\mathrm{n}}_{\mathrm{g}}$ or, ${\mathrm{n}}_{\mathrm{d}}=1.6\times 1.5=2.4$
as a result, diamond's refractive index is 2.4

Hence, the correct answer is option C.