For photoelectric effect, the stopping potential depends on

The work function of metals is in the range of $2 \mathrm{eV}$ to $5 \mathrm{eV}$. Find which of the following wavelength of light cannot be used for the photoelectric effect. (Consider, $\mathrm{Planck} \mathrm{constant}=4\times {10}^{-15}\mathrm{eVs},$   $\mathrm{velocity} \mathrm{of} \mathrm{light} =\left.3\times {10}^8\mathrm{m} {\mathrm{s}}^{-1}\right)$ 

Assertion: Work function of a metal is proportional to maximum wavelength of the photons incident.

Reason: Work function is given by the relation, ${\varphi }_0=\frac{hc}{{\lambda }_{\text{max}}}$.