The work function $\left(\varphi \right)$ 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
$\Phi \left(eV\right)$	2.4	2.3	2.2	3.7	4.8	4.3	4.7	6.3	4.75

 

Energy of photon $=\frac{hc}{\lambda }J=\frac{hc}{e\lambda }eV=\frac{6.625\times {10}^{-34}\times 3\times {10}^8}{300\times {10}^{-9}\times 1.602\times {10}^{-19}}=4.14eV$

For photoelectric effect to occur, energy of incident photons must be greater than work function of metal. Hence, only $Li,Na,K$ and $Mg$ have work functions less than $4.14V.$