Question

Which of the following is a redox reaction, but not a combination reaction?

• A. C + O₂ → CO₂
• B. H₂ + O₂ → H₂O
• C. Mg + O₂ → MgO
• D. Fe₂O₃ + 3 CO → 2 Fe + 3 CO₂

Answer 1

The Correct Option is D

To determine which reaction is a redox reaction but not a combination reaction, we must understand the definitions:

• A redox reaction involves the transfer of electrons between two species. It consists of two half-reactions: oxidation (loss of electrons) and reduction (gain of electrons).
• A combination reaction is a type of chemical reaction where two or more substances combine to form a single new compound.

Let's analyze each given reaction:

• C + O₂ → CO₂: This is a redox reaction where carbon is oxidized, and oxygen is reduced. However, it is also a combination reaction, as carbon and oxygen combine to form CO₂.
• H₂ + O₂ → H₂O: Similar to the first reaction, this is a redox reaction where hydrogen is oxidized and oxygen is reduced. It is also a combination reaction, forming water from hydrogen and oxygen.
• Mg + O₂ → MgO: This reaction involves the oxidation of magnesium and reduction of oxygen. It is a combination reaction, as magnesium and oxygen form MgO.
• Fe₂O₃ + 3 CO → 2 Fe + 3 CO₂: This is a redox reaction. Iron (Fe) is reduced from Fe₂O₃ to Fe, and carbon monoxide (CO) is oxidized to CO₂. It is not a combination reaction because it doesn't involve two or more reactants forming a new single product; instead, it involves the reduction of iron ore and oxidation of CO, resulting in multiple products.

Therefore, the reaction Fe₂O₃ + 3 CO → 2 Fe + 3 CO₂ is a redox reaction that is not a combination reaction.