Question

A monochromatic beam of light is absorbed by a collection of ground-state hydrogen atoms in such a way that three different wavelengths are observed when the hydrogen relaxes back to the ground state.

Answer 1

If the absorbed beam is monochromatic (one wavelength) then it excites the H atom to some state n.

When that state decays, some of the atoms may decay to state 1, others to state 2, and still others to state 3

The net energy emitted in such a case would depend on:

n -1, n - 2, n - 3 which would produce 3 different wavelengths