Carbon reduces oxides of metals below it in the reactivity series

Steps:

• Recall the reactivity series ranks metals by reactivity: K, Na, Ca, Mg, Al above carbon; Zn, Fe, etc., below.
• Carbon acts as a reducing agent for oxides of less reactive metals (below carbon).
• Check positions: Al, Ca, Mg are above carbon, so their oxides resist reduction by carbon.
• Zn is below carbon, allowing ZnO reduction via heating with carbon.

Why D is correct:

• ZnO + C → Zn + CO; zinc's position below carbon enables this thermite-like reduction.

Why the others are wrong:

• A. Aluminium oxide (Al₂O₃) is highly stable, requiring electrolysis for reduction.
• B. Calcium oxide (CaO) is basic and unreactive with carbon; needs electrolysis from CaCl₂.
• C. Magnesium oxide (MgO) has a strong lattice, not reduced by carbon; uses electrolysis.

Final answer: D