The threshold wavelength for photoelectric emission from a material is 5200∘A. Photo-electrons will be emitted when this material is illuminated with monochromatic radiation from a
Both (c) and (d)
In this case, for photoelectric emission the wavelength of incident radiations must be less then 5200∘A . Wavelength of ultraviolet radiations is less then this value (5200∘A) but wavelength of infrared radiations is higher than this value.