A hydrogen atom emits green light when it changes from the n=4 energy level to n=2 energy level. Which colour of light would the atom emit when it changes from the n=5 level to n=2 level?

A.Red
B.Yellow
C.Green
D.Violet

Hint: We know that the energy of photons of light emitted by a hydrogen atom when it changes from n=4 energy level to n=2 energy level is equal to the potential energy difference between energy level n=4 and n=2. Also, we know that the colour of light depends on the energy of the photon. VIBGYOR pattern is the decreasing order of energy of light.

Complete step by step answer:
Given, a hydrogen atom emits green light when it changes from the n=4 energy level to n=2 energy level. It means the energy difference in energy level is equal to the energy of green light.
We know that colour of light id depends on the energy of light or difference in energy of initial and final energy level. In VIBGYOR, colours are arranged in decreasing order of energy.
If hydrogen changes its state from n=5 energy level to n=2 then the energy of light emitted is greater than the energy of light emitted when it changes from the n=4 energy level to n=2 energy level.
It means the energy of light emits when hydrogen changes its state from n=5 energy level to n=2 is greater than green colour.
In the given option, only violet colour has more energy than green colour.
Hence the correct answer is option D (violet).

Note:When we provide energy to hydrogen then its state changes from lower state to higher energy state. And it changes its state from higher energy level to lower energy level by releasing light energy in the form of electromagnetic waves.