Identify the oxidising agent (oxidant) in the following reactions:
$(a) Pb_{3}O_{4} + 8HCl \longrightarrow 3PbCl_{2} + Cl_{2} + 4H_{2}O$
$(b) 2Mg + O_{2} \longrightarrow 2MgO$
$(c) CuSO_{4} + Zn \longrightarrow Cu + ZnSO_{4}$
$(d) V_{2}O_{5} + 5Ca \longrightarrow 2V + 5CaO$
$(e) 3Fe + 4H_{2}O \longrightarrow Fe_{3}O_{4} + 4H_{2}$
$(f) CuO + H_{2} \longrightarrow Cu + H_{2}O$

(A) An oxidising agent is a substance that gains electrons or provides oxygen (or removes hydrogen) in a chemical reaction.
$(a) Pb_{3}O_{4}$: Lead is reduced from $+8/3$ to $+2$,so $Pb_{3}O_{4}$ acts as the oxidising agent.
$(b) O_{2}$: Oxygen is reduced from $0$ to $-2$,so $O_{2}$ acts as the oxidising agent.
$(c) CuSO_{4}$: Copper is reduced from $+2$ to $0$,so $CuSO_{4}$ acts as the oxidising agent.
$(d) V_{2}O_{5}$: Vanadium is reduced from $+5$ to $0$,so $V_{2}O_{5}$ acts as the oxidising agent.
$(e) H_{2}O$: Hydrogen is reduced from $+1$ to $0$,so $H_{2}O$ acts as the oxidising agent.
$(f) CuO$: Copper is reduced from $+2$ to $0$,so $CuO$ acts as the oxidising agent.