Answer: a) Sn 2+
Explanation:A reducing agent is a substance that can be oxidized when it loses electrons while An oxidizing agent is a substance that is reduced when it gains electrons.
Considering Cu 2+, Fe 3+, Al 3+, Here, Cu 2+ can be reduce to its Copper metal, same for Al 3+ to Aluminium metal and Fe 3+ to Fe 2+ ion and will not be oxidized further since they are in their most oxidized states. The three ions are acting as only oxidizing agents.
while Sn 2+ can be oxidized to become Sn 4+ and also be reduced to become Sn metal acting as a reducing agent and an oxidizing agent.
