Dual Nature of Radiation

The threshold wavelength for photoelectric emission from a material is 5500 $$\mathop A\limits^o$$. Photoelectrons will be emitted, when this material is illuminated with monochromatic radiation from a A. 75 W infra-red lamp B. 10 W infra-red lamp C. 75 W ultra-violet lamp D. 10 W ultra-violet lamp Choose the correct answer from the options given below :