The correct option is A 2
The given compound is an ionic compound which is made up of one magnesium and two chlorine atoms.
Chloride ion always has a unit negative charge.
Since ionic compounds are neutral in nature, the net charge on them is zero.
⟹Charge on magnesium ion + 2×(charge on chloride ion) = 0
⟹Charge on magnesium ion + 2×(-1) = 0
⟹Charge on magnesium ion = +2
Thus, magnesium has two units positive charge, written as Mg2+.