Photo-electric effect can be explained by

There are two sources of light, each emitting with a power of $100 \,W.$ One emits $X-$ rays of wavelength $1\, nm$ and the other visible light at $500\, nm$. Find the ratio of number of photons of $X-$ rays to the photons of visible light of the given wavelength ? 

In a dark room of photography, generally red light is used. The reason is

Assertion : Photoelectric effect demonstrates the wave nature of light.
Reason : The number of photoelectrons is proportional to the frequency of light.

Monochromatic light of wavelength $667 \,\,nm$ is produced by a helium neon laser. The power emitted is $9 \,\,mW.$ The number of photons arriving per sec. on the average at a target irradiated by this beam is

When light falls on a metal surface, the maximum kinetic energy of the emitted photo-electrons depends upon