The question is incomplete. Complete question is attached below.
Solution:The reaction involved in present case is shown below:
Mg(s) + Zn2+(aq.) ↔ Zn(s) + Mg2+ (aq.)
From the above reaction, it is clearly evitable that 1 mole of Zn2+ reacts with 1mole of Mg to produce 1 mole of Mg2+.
Thus, 2.5 moles of Zn2+ reacts with 2.5 moles of Mg to produce 2.5 moles of Mg2+
