The energy required to overcome the attractive forces on the electrons, w, of some metals is listed below . The number of metals showing photoelectric effect when light of 300 nm wavelength falls on it is :

Question

$ ( 1\: eV = 1.6 \times 10^{-19}J)$

Metal   :     Li      Na      K      Mg      Cu      Ag     Fe      Pt     W

w (eV) :     2.4    2.3     2.2     3.7      4.8     4.3    4.7    6.3   4.75

$\begin {array} {1 1} (1)\;6 & \quad (2)\;8 \\ (3)\;5 & \quad (4)\;4 \end {array}$