The following are spontaneous reactions. List the species in these reactions in the order of oxidizing strength, from the strongest to weakest oxidizing agent:
2 Cr2+ + Sn2+ Sn + 2 Cr3+
Fe + Sn2+ Sn + Fe2+
Fe + U4+ No reaction
U3+ + Cr3+ U4+ + Cr2+
Fe + 2 Cr3+ Fe2+ + 2 Cr2+