A hydrogen atom in its ground state absorbs a photon. In the process an electron is excited to a higher state. The atom will then most likely (A) emit a photon. (B) remain in the excited state. (C) become ionized. (D) split in half. (E) collide with another atom.

We first need to understand the possible outcomes for an excited-electron hydrogen atom: 1) Emit a photon: The electron returns to a lower energy level, releasing a photon in the process. 2) Remain in the excited state: The electron stays in the higher energy level. 3) Become ionized: The electron is ejected from the atom due to excess energy, resulting in a positive ion. 4) Split in half: Since atoms do not typically split, this option is unlikely. 5) Collide with another atom: The atom may interact with another atom, but this is unrelated to the electron's excitation.

Now, let's evaluate the probabilities of the outcomes: 1) Emit a photon: This is the most common outcome, as excited electrons tend to release excess energy in the form of photons and return to a lower energy state. 2) Remain in the excited state: This outcome is possible, but given the spontaneous nature of excited electrons returning to lower energy states, it is less likely than emitting a photon. 3) Become ionized: While possible, ionization requires a much higher energy input than just exciting an electron to a higher state within the atom. Thus, this outcome is less likely than emitting a photon. 4) Split in half: As previously mentioned, atoms do not typically split in half, so this outcome is highly unlikely. 5) Collide with another atom: Although two atoms may collide, it doesn't have a direct relationship with the electron's excitation and isn't a consequence of the absorbed photon.

Based on our evaluation, the most likely outcome for a hydrogen atom with an excited electron is to emit a photon (option A). This is because the other outcomes are either less probable or unrelated to the electron's excitation. Answer: (A) emit a photon.