The wave length of $1kev$ photon is $1.24 \times 10^{-9}\;m$. What is the frequency of $1Mev$ photon ?

Question

$\begin{array}{1 1} 1.2 \times 10^{15} \\ 2.4 \times 10^{20} \\ 1.24 \times 10^{18} \\ 2.4 \times 10^{23} \end{array}$