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 (positive charge) and electrons (negative charge). When it gains an electron, the number of negative charges (electrons) exceeds positive charges (protons). So it becomes negatively charged.

• Losing a proton is not related to gaining an electron.
• Gaining one electron doesn't necessarily attract more electrons.
• Electron's mass is negligible compared to proton and neutron, so atomic mass (sum of protons, neutrons and electrons) increase is negligible (not a significant change as per common understanding in basic atomic structure concepts).

Answer:

The atom becomes negatively charged.