The work function ($\mathrm{\varphi }$) of some metals is listed below. The number of metals which will show photoelectric effect when light of 300 nm wavelength falls on the metal is 

$\text{ The energy associated with incident photon }=\frac{\mathrm{hc}}{\mathrm{\lambda }}$

$\begin{array}{l}\Rightarrow \mathrm{E}=\frac{6.6\times {10}^{-34}\times 3\times {10}^8}{300\times {10}^{-9}}\mathrm{J}\\ \mathrm{E}\text{ in }\mathrm{eV}=\frac{6.6\times {10}^{-34}\times 3\times {10}^8}{300\times {10}^{-9}\times 1.6\times {10}^{-19}}=4.16\mathrm{eV}\end{array}$

So, number of metals showing photo-electric effects will be 
(4), i.e., Li, Na, K, Mg