Determine the number of electrons in an Cl ion with a charge of -3

There are 20 electrons.

Explanation:

Chlorine has 17 electrons in its atom to begin with (you can tell from the proton number in the periodic table).

A charge of -3 means that the chlorine atom gained 3 electrons, and now needs to lose 3 electrons to return to its atom configuration.

answer is a

explanation:

increased stability in the completion of fluorine's outer shell.