Reactivity series determines metal displacement and reduction

Steps:

• Identify series: potassium > aluminium > zinc > copper (hydrogen below copper).
• More reactive metals displace less reactive from compounds; hydrogen reduces oxides of metals below it.
• Test options: displacement requires higher reactivity; reduction by H2 for metals less reactive than H.
• Verify C: hydrogen reduces CuO as copper is below hydrogen.

Why C is correct:

• Copper(II) oxide reduces with hydrogen (CuO + H₂ → Cu + H₂O) since copper is less reactive than hydrogen.

Why the others are wrong:

• A: Aluminium above hydrogen, so hydrogen cannot reduce Al₂O₃ to Al.
• B: Copper less reactive than zinc, so cannot displace Zn from ZnSO₄.
• D: Potassium more reactive than aluminium, so forms K⁺ ions more readily with water.

Final answer: C