Which term means "a charged atom that has either gained or lost a negative charge"?

A) neutron

B) proton

C) electron

D) ion

D) ion

The term that means "a charged atom that has either gained or lost a negative charge" is an ion.

To determine the correct answer to this question, you can break down the options and their definitions:

A) A neutron is a subatomic particle with no charge.

B) A proton is a subatomic particle with a positive charge.

C) An electron is a subatomic particle with a negative charge. However, in this case, the question is asking about a charged atom, not just a negatively charged particle.

D) An ion is an atom or group of atoms that has gained or lost electrons, resulting in a positive or negative charge, respectively. This definition matches the description provided in the question.

Therefore, the correct answer is D) ion.