(D) Fe₂O₃ + 3CO → 2Fe + 3CO₂
In this reaction, CO is oxidised (gains oxygen) and Fe₂O₃ is reduced (loses oxygen), making it a redox reaction. It is not a combination reaction as two reactants give two products.
Options A, B, and C are both combination reactions (two reactants forming one product) AND redox reactions. Option D involves two reactants giving two products, so it is not a combination reaction, but it is a redox reaction because CO gets oxidised to CO₂ and Fe₂O₃ gets reduced to Fe. Examiners expect you to know both criteria to eliminate the wrong options.