Question

an atom becomes an ion with a -1 charge because the atom gains one electron. loses one electron. gains one proton. loses one proton.

Explanation:

In an atom, electrons are negatively charged. When an atom gains one electron, it has one more negative charge than positive charges (protons). This results in a net charge of -1, forming an ion with a -1 charge. Losing an electron would give a positive charge (since there would be more protons than electrons), and changing the number of protons changes the element itself, not just the charge of the atom (as protons are in the nucleus and define the element).

Answer:

A. gains one electron.