Question

what causes an atom to have a negative charge? it gains an electron. it loses a proton. it loses an electron. it gains a proton.

Explanation:

An atom is neutral when it has equal numbers of protons (positive charge) and electrons (negative charge). If it gains an electron, there are more electrons (negative) than protons (positive), resulting in a negative charge. Losing a proton would change the element (as the number of protons defines the element) and also make the charge more positive (since there's one less positive charge). Losing an electron makes the atom positively charged (more protons than electrons). Gaining a proton changes the element and makes the charge more positive.

Answer:

It gains an electron.