How many electrons are in an atom of chlorine with a - 1 charge? 17 16 18 8

18

Explanation:

The atomic number of chlorine is 17 therefore the atom has 17 electrons, the ion however has 1 extra electron. The charge becomes negative because electrons have a negative charge. 17 + 1 = 18, therefore a chlorine ion with a charge of - 1 has 18 electrons.