Final answer:
A fluorine cation, which is a positively charged ion, gains electrons to become neutral or stabilize its electronic configuration. It is the correct answer (c) among the given options.
Step-by-step explanation:
The student has asked which of the following gains electrons: a) fluorine isotope, b) fluorine gas, c) fluorine cation, d) fluorine anion, or e) fluorine. The answer is c) fluorine cation. When an atom gains electrons, it becomes an anion, which means it will have a negative charge. A fluorine cation represents a positively charged fluorine ion that has lost an electron, but in order to become neutral or form a stable configuration, it must gain the electron it previously lost.
For example, a neutral fluorine atom, with an atomic number of 9, has seven electrons in its valence shell and by gaining one more electron, it achieves a stable electron configuration that mimics the noble gas neon. The resultant ion with this added electron is the fluoride anion (Fˉ).