The answer is A.
Chlorine is found in group7A of the periodic table. This means that when they are neutral, (electrons and protons are equal), they lack 1 electron to complete the octet or eight valence electrons to be stable. This will result in Chlorine having to gain an electron. Since it gained an electron, that means the electrons outnumber the protons by 1, which will result in a negative charge of -1.
