d
\(1s\) electronic level would allow the hydrogen atom to absorb a photon but not to emit it. On absorption of radiation, electron will be transferred from is level to higher level such as \(2 s\) or \(3 s\). But to emit a photon, the electron should go to the lower energy level from higher energy level. Since is is the lowest energy level, the electron cannot go to a lower level. Hence, emission is not possible.