Final answer:
Correct option: b) The hydrogen atom in an excited state.
A photon of energy can cause a hydrogen atom to go into an excited state, and if another one collides while it's still excited, and the energy is high enough, it could potentially ionize the atom. Following excitation, the atom can return to the ground state, emitting photons that correspond to the energy difference between the energy levels. The duration an atom stays excited varies, with some transitions being quick and others taking much longer.
Step-by-step explanation:
When a photon of energy collides inelastically with a hydrogen atom, it may transfer some of its energy to the electron within the atom, causing the electron to jump to a higher energy level, this process is known as excitation. If a second photon collides with the atom while it is still in this excited state, and if the energy is sufficient, it can either raise the electron to an even higher energy state, or if the energy exceeds the ionization energy of the atom, it can remove the electron entirely, leading to ionization. The outcomes of the collisions depend on the energy levels of the photons and the current state of the hydrogen atom.
After excitation, the atom can return to its ground state through different pathways. The atom may return to its lowest state in one jump, emitting a photon, or it may transition in steps, stopping at intermediate levels, and emit multiple photons. The emitted photons correspond to the energy difference between the energy levels involved in the transitions.
If no collisions occur that might prompt a quicker de-excitation, an excited hydrogen atom can remain in the higher energy state for an extended period before it emits a photon and returns to the ground state. The durations vary with different transitions; some are very quick, happening in microseconds, while others, such as those emitting a 21-centimeter radio wave, can take much longer.