Answer: 2.5 moles of Mg+2
Since it is an example for intermolecular redox reaction. Here Mg gets oxidized to Mg+2 and Zn+2 gets reduced to Zn.
Mg(s)+ Zn+2(aq) -------> Mg+2(aq) + Zn(s)
From the balanced equation, 1:1 molar ratio of Mg and Zn+2. Hence 2.5 moles of Zn+2 produce 2.5 moles of Mg+2.