Answer
Mg is oxidized.
Sn²⁺ is reduced
Step-by-step explanation
Given equation:
Mg(s) + Sn²⁺(aq) → Mg²⁺(aq) + Sn(s)
An oxidizing agent is a substance that causes oxidation by accepting electrons; therefore, it gets reduced. A reducing agent is a substance that causes reduction by losing electrons; therefore it gets oxidized.
From the given equation, the oxidation of Mg changes from 0 to +2, while the oxidation number of Sn changes from +2 to 0.
Therefore, Mg is oxidized, and Sn²⁺ is reduced.