Answer:
The charge would be -1.
Step-by-step explanation:
The atomic number refers to the number of protons an atom has. Chlorine is electrically neutral, so it has the same number of positive charges (protons) than negative charges (electrons). Therefore, chlorine has 17 protons and 17 electrons. When it gains 1 electron, it will have an excess of one negative charge, so the charge of the ion will be -1, forming Cl⁻.