How many chloride ions are needed to cancel the +2 charge of magnesium in magnesium chloride?

The correct option is B 2
Two chloride ions are required to cancel the +2 charge of magnesium in magnesium chloride because magnesium chloride is an ionic compound in which $Mg$ atom changes to $M{g}^{2+}$ cation by losing two valence electrons. Each $Cl$ atom changes to $C{l}^{-}$ 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: $Mg-2e^{-}\to M{g}^{2+}$, $C{l}_2+2e^{-}\to 2C{l}^{-}$