A photocell is operating in saturation mode with a aphotocurrent 4.8mA when a monochromatic radiation of wavelength $\;3000A^{0}\;$ and power 1mW is incident. When another monochromatic radiation of wavelength $\;1650A^{0}\;$ and power 5mW is incident , it is observed that maximum velocity of photoelectron generation per incident to be same for both cases . Than the threshold wavelength for cell is :

Question

$(a)\;5268A^{0}\qquad(b)\;3128A^{0}\qquad(c)\;1264A^{0}\qquad(d)\;4133A^{0}$