Final answer:
A sodium ion (Na-) has gained an extra electron compared to the neutral sodium atom, resulting in a total of 12 electrons.
Step-by-step explanation:
A sodium ion with a notation Na- indicates that it has gained an extra electron compared to the neutral sodium atom. A neutral sodium atom, represented by the symbol Na, has 11 protons and 11 electrons, giving it zero overall charge. When a sodium atom becomes a sodium ion with a negative charge (Na-), it has gained an electron in addition to the 11 it already had. Therefore, a Na- ion has 12 electrons.