The difference between threshold wavelengths for two metal surfaces $\mathrm{A}$ and $\mathrm{B}$ having work function $\phi_{A}=9 ~\mathrm{eV}$ and $\phi_{B}=4 \cdot 5 ~\mathrm{eV}$ in $\mathrm{nm}$ is:

$\{$ Given, hc $=1242 ~\mathrm{eV} \mathrm{nm}\}$