Reactivity series governs displacement and reduction reactions

Steps:

• Note the series: potassium > aluminium > zinc > copper > hydrogen.
• More reactive elements displace less reactive ones from compounds.
• Hydrogen reduces oxides of metals below it in the series.
• Evaluate options using these rules.

Why C is correct:

• Copper is below hydrogen, so hydrogen acts as a reducing agent: CuO(s) + H₂(g) → Cu(s) + H₂O(g).

Why the others are wrong:

• A: Aluminium is above hydrogen, so hydrogen cannot reduce Al₂O₃ to Al.
• B: Copper is below zinc, so copper cannot displace zinc from ZnSO₄(aq).
• D: Potassium is above aluminium, so potassium forms K⁺ ions more readily than Al³⁺ in water.

Final answer: C