Final answer:
Among the options given, Mg(s) is the strongest reducing agent, indicated by its position above aluminum and zinc in the activity series of metals.
Step-by-step explanation:
The question which of the following is the strongest reducing agent is focused on identifying the substance with the greatest tendency to donate electrons in a chemical reaction. Among Zn(s), Mg(s), Al(s), and Al³⁺(aq), Mg(s) is generally considered the strongest reducing agent.
This is substantiated by the activity series of metals, which typically lists magnesium above aluminum and zinc, indicating its greater tendency to lose electrons and thus its stronger reducing property. An example of this is the electrolysis process, where magnesium would be reduced at the cathode.
The strength of a reducing agent can also be related to its position in the electrochemical series and its standard electrode potential.
While Al³⁺(aq) is not generally considered a reducing agent due to its already oxidized state, solid elemental forms of metals, such as Mg(s), can readily lose electrons and act as strong reducing agents.