A photosensitive metallic surface is illuminated alternately with lights of wavelength 3100 Å and 6200 Å. It is observed that maximum speeds of the photoelectrons in two cases are in ratio 2 : 1. The work function of the metal is (hc = 12400 eVÅ)
(1) 1 eV                  (2) 2 eV                 (3) $\frac{4}{3}$ eV              (4) $\frac{2}{3}$ eV