Answer:
An Mg atom donates one electron to each of the two Cl atoms.
Explanation:
Chlorine is a non-metal halogen and does not have the ability to donate electrons, on the contrary, it picks them up. In fact it is almost the most electronegative of the periodic table, below the fluoride that is the most.
The chlorine then accepts one electron per magnesium to form the magnesium chloride being its formula MgCl2.
Magnesium is a metal of group two and it does yield electrons, in this case it can only yield 2 (group 2 of the Periodic Table) forming the Mg 2+ cation
Mg2+ + 2Cl- ------> MgCl2
