The speed of light in air is $3\times {10}^8$ m/s and the speed of light in common glass is  $2\times {10}^{8 }$m/s. Refractive index of glass will be:

The formula may be used to determine the refractive index of any media., $\frac{\sin {\theta }_1}{\sin {\theta }_2}=\frac{v_1}{v_2}=\frac{n_2}{n_1}=n_{21}$. Now that we have the numbers for the speeds of light in air and glass, we can use this formula to get the refractive index of glass.

The difference between the speed of light in glass and the speed of light in a vacuum is known as the refractive index of glass.
Glass's index of refraction, ${\mathrm{n}}_{\mathrm{g}}=\frac{\text{ Speed of light in vacuum }}{\text{ Speed of light in glass }}$
Therefore, ${\mathrm{n}}_{\mathrm{g}}=\frac{3\times {10}^8}{2\times {10}^8}=\frac{3}{2}$.

Hence, the correct answer is option C.