If an electron is gained, the atom has a charge.

positive
negative

The correct answer for the fill in the blank is Negative.

There are three subatomic particles of an atom that are electron ( negatively charged), proton ( positively charged), and neutron ( with no charge). This means that electron is a negatively charged ion.

If an atom gains an electron, it means that there is an increase in its negative charge.

Thus, the atom has a negative charge.            

energy and particles