When a light of wavelength $300\: nm$ falls on a photoelectric emitter, the photoelectrons are liberated. For another emitter, the light of wavelength $600\: nm$ is sufficient for liberating photoelectrons. The ratio of the work function of the two emitters, is

Question

$\begin {array} {1 1} (a)\;1:2 & \quad (b)\;2:1 \\ (c)\;4:1 & \quad (d)\;1:4 \end {array}$