1. Red light of wavelength $750 nm$ enters a glass plate of refractive index $1.5$. If the velocity of light in vacuum is $3 \times 108 m/s$, then its frequency is

Question

$\begin{array}{1 1} (a)\; 40 \times 10^{14} Hz \\b)\; 4 \times 10^{14} Hz \\ c)\; 40 \times 10^{13} Hz \\ d)\; 4 \times 10^{13} Hz \end{array}$