The correct answer is: A. Gamma-emission
In gamma-emission, a radioactive atom emits a high-energy photon, or gamma ray, from its nucleus. The atom’s mass and charge remain unchanged.
Alpha-emission occurs when a radioactive atom emits an alpha particle, which is a helium nucleus consisting of two protons and two neutrons. The atom’s mass decreases by four units and its charge decreases by two units.
Beta-emission occurs when a radioactive atom emits a beta particle, which is an electron or a positron. The atom’s mass remains unchanged, but its charge increases by one unit if the beta particle is an electron, or decreases by one unit if the beta particle is a positron.
Oxidation is a chemical reaction in which an atom or molecule loses electrons. This can occur when a radioactive atom reacts with oxygen, or when it is exposed to other oxidizing agents. Oxidation can cause the radioactive atom to lose mass and charge.
Therefore, the only option that does not result in a change in the mass or charge of the radioactive atom is gamma-emission.