Answer:
Mg2+
Explanation:
The most reactive ions from the given choices is the magnesium ion. This is because it is higher in the activity series of metals.
Zinc ion is below this specie in the activity series.
As a rule, ions above another on the activity series are generally more reactive than those below.
From any solution, magnesium ion will displace the zinc ion in such process.
The position of metallic ions determines their reactivity.
