The work function of the following metals are : $Na = 2.75\: eV; K = 2.3\: eV ; Mo = 4.17\: eV ; Ni = 5.15 \: eV$. Which of these metals will not give photoelectric emission for a radiation of wavelength $3300\: A^{\circ}$ the photocell? from a $He – Cd$ laser placed $1m$ away from

Question

$\begin {array} {1 1} (a)\;Mo,Ni & \quad (b)\;Na,Ni \\ (c)\;Ni,K & \quad (d)\;Na,K \end {array}$