The ratio of the energy of a photon of 2000 $\stackrel{\mathrm{o}}{\mathrm{A}}$ wavelength radiation to that of 4000 $\stackrel{\mathrm{o}}{\mathrm{A}}$ radiation is 

To find the ratio of the energy of a photon to the radiation, let us find E_1​ and E_2​
$$\begin{gathered} \mathrm{E}=\frac{\mathrm{hc}}{\mathrm{\lambda }} \\ \Rightarrow \frac{{\mathrm{E}}_1}{{\mathrm{E}}_2}=\frac{{\mathrm{\lambda }}_2}{{\mathrm{\lambda }}_1} \end{gathered}$$
Thus, we have the ratio of energies​​.$\frac{{\mathrm{E}}_1}{{\mathrm{E}}_2}=2$