The work function $\left(\mathrm{\varphi }\right)$ 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 
 

Metal	Li	Na	K	Mg	Cu	Ag	Fe	Pt	W
$\varphi$(eV)	2.4	2.3	2.2	3.7	4.8	4.3	4.7	6.3	4.75

Energy of photon
$\frac{\mathrm{hc}}{\mathrm{\lambda }}\mathrm{J}=\frac{\mathrm{hc}}{\mathrm{e\lambda }}\mathrm{eV}=\frac{6.625\times {10}^{-34}\times 3\times {10}^8}{300\times {10}^{-9}\times 1.602\times {10}^{-19}}=4.14\mathrm{eV}$
For photoelectric effect to occur, energy of incident photons must be greater work function of metal. Hence, only Li,Na,K and Mg have work functions less than 4.14 V