Answer : When the number of photons increases, the brightness of the beam of light increases.
Explanation :
According to Einstein's theory,

Where,
n is the no of photons.
h is the Plank's constant
is the frequency of light.

So, the number of photon depends directly on the total energy of the group of photons and inversely on the frequency.
Out of given options, the correct one can be (c) or (e). But in (e), it is written that the energy of each photon increases. This is wrong because the total energy of the photon should increase.
Hence, the correct option is (c) "The brightness of the beam of light increases".