Q.In the reaction $\text{Zn}(s) + \text{CuSO}_4(aq) \to \text{ZnSO}_4(aq) + \text{Cu}(s)$, identify the oxidizing agent and the reducing agent, and state the classical reasoning for your choice.

[!TLDR] Zinc loses electrons to $\text{Cu}^{2+}$, so zinc is the reducing agent and copper(II) sulfate (via $\text{Cu}^{2+}$) is the oxidizing agent. [!ANSWER] Reducing agent: $\text{Zn}$; oxidizing agent: $\text{CuSO}_4$ (its $\text{Cu}^{2+}$ ion).

In $\text{Zn}(s) + \text{CuSO}_4(aq) \to \text{ZnSO}_4(aq) + \text{Cu}(s)$, zinc metal is converted to $\text{Zn}^{2+}$ ions in solution, while $\text{Cu}^{2+}$ ions are converted to metallic copper. Zinc is oxidized (it loses electrons, going from oxidation number $0$ to $+2$), so it is the substance that supplies electrons to the other reactant — this makes zinc the reducing agent. The $\text{Cu}^{2+}$ ion, supplied by $\text{CuSO}_4$, is reduced (it gains electrons, going from $+2$ to $0$), so it is the substance that accepts electrons from zinc — this makes copper(II) sulfate (specifically its $\text{Cu}^{2+}$ ion) the oxidizing agent. This matches the general rule that the reducing agent is always the species oxidized, and the oxidizing agent is always the species reduced. [!ANSWER] Reducing agent: $\text{Zn}$; oxidizing agent: $\text{CuSO}_4$ (its $\text{Cu}^{2+}$ ion).

Track which reactant loses electrons (becomes more positively charged) and which gains electrons (becomes less positively charged); the electron-loser is the reducing agent, the electron-gainer is the oxidizing agent.

Swapping the labels — calling the species that is itself oxidized the 'oxidizing agent' rather than the 'reducing agent'.