Final answer:
Electron affinity is the energy change that occurs when an electron is added to a neutral atom, creating an anion, typically resulting in energy release. The values become more negative across the periodic table and less negative within a group. Halogens release more energy during anion formation due to their high electron affinity.
Step-by-step explanation:
Electron affinity refers to the energy change that occurs when an electron is added to a gaseous atom to form an anion, which is answer A. Adding an electron to a neutral atom typically causes energy to be released. This is because the electron is being incorporated into an existing electrical field, and when it moves closer to the nucleus, energy is given off. The general trend for electron affinity values across the periodic table is that they become more negative as you move from left to right, due to increased nuclear charge. When moving down a group, electron affinities generally become less negative due to the increased distance of the outer shell from the nucleus.
The definition provided by the student applies to the process of the addition of an electron to a neutral atom, effectively resulting in the creation of a negative ion (anion). In the case of halogens, such as chlorine, more energy is released during the formation of a halide ion because they have a high electron affinity; they are just one electron short of completing their valence shell and reaching a stable noble gas configuration.