The work function of a surface of a photosensitive material  is 6.2 eV. The wavelength of the incident radiation forwhich the stopping potential is 5 eV lies in the

According to laws of photoelectric effectKEmax=E−ϕwhere  ϕ  is  work  function  and  KEmax,  is  maximum,kinetic  energy  of  photoelectron.∴hv=eVo+ϕor   hv=5eV+6.2eV=11.2eV∴λ=1240011.2Ao≈1000AoHence, the radiation lies in ultraviolet region.