The correct option is B 2
Two chloride ions are required to balance the +2 charge of magnesium in magnesium chloride because magnesium chloride is an ionic compound in which Mg atom changes to Mg2+ cation by losing two valence electrons. Each Cl atom changes to Cl− anion by gaining one electron which resembles the configuration of next noble gas, argon. To balance the two positive charge of magnesium, two chlorine atoms are required or two chloride ions are required.
The equation: Mg−2e−→Mg2+, Cl2+2e−→2Cl−