Question

what happens when an atom gains an electron?
the atom loses a proton.
the atom attracts additional electrons.
the atom increases in atomic mass.
the atom becomes negatively charged.

Explanation:

An atom is neutral with equal number of protons (positively - charged) and electrons (negatively - charged). When it gains an electron, there are more negative charges than positive charges, so it becomes negatively charged. Protons are not lost when an electron is gained. Gaining one electron does not necessarily attract more electrons. The mass of an electron is negligible compared to protons and neutrons, so gaining an electron does not significantly increase atomic mass.

Answer:

The atom becomes negatively charged.