Which one of the following is a reduction reaction?
[amp_mcq option1=”2 Mg (s) + O₂ (g) → 2 MgO (s)” option2=”S (s) + O₂ (g) → SO₂ (g)” option3=”2 HgO (s) $\xrightarrow{heat}$ 2 Hg (l) + O₂ (g)” option4=”Mg (s) + S (s) → MgS (s)” correct=”option3″]
This question was previously asked in
UPSC NDA-1 – 2016
A) 2 Mg (s) + O₂ (g) → 2 MgO (s): Mg is oxidized (0 to +2), O₂ is reduced (0 to -2).
B) S (s) + O₂ (g) → SO₂ (g): S is oxidized (0 to +4), O₂ is reduced (0 to -2).
D) Mg (s) + S (s) → MgS (s): Mg is oxidized (0 to +2), S is reduced (0 to -2).
All listed reactions are redox reactions involving both oxidation and reduction. However, option C specifically shows the reduction of a metal cation (Hg²⁺) to its elemental form (Hg⁰) by the loss of oxygen from its compound, making it a clear example of a reduction process relative to the metal. The question asks which *one* is *a* reduction reaction, and while all involve reduction, C best exemplifies the reduction of the stated element (Hg).