What is the charge of Mg in MgCl2 ?
2+
The net charge on an ionic compound is zero.
Cl− ion always has a unit negative charge.
The charge on Magnesium ion can be calculated as:
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+.