$A$ light of wavelength $\lambda_{1}$ and velocity $C_{1}$ travels from the first medium of refractive index $\mu_{1}$ into the second medium of refractive index $\mu_{2}$. The wavelength and velocity of light in the second medium are $\lambda_{2}$ and $C_{2}$ respectively. The refractive index of the second medium with respect to the first medium is given by:

• A
  $\frac{C_{2}}{C_{1}}$
• B
  $\frac{\mu_{2}}{\mu_{1}}$
• C
  $\frac{\mu_{1}}{\mu_{2}}$
• D
  $\frac{\lambda_{2}}{\lambda_{1}}$