The work function ( $\varphi$ ) 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   Metal

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

Since the value of  $hc=1240eVnm$
Energy corresponding to $\lambda =300$  nm is 
$\frac{1240eVnm}{300nm}=4.134eV$
Elements having $\varphi <4.134eV$ will show photoelectric  effect, are Li, Na, K, and Mg $\Rightarrow \boxed{4}$  
So, number of metals showing photo –electric will be four, i.e., Li, Na, K,  and Mg.