Which one of the following is a reduction reaction?
2 Mg (s) + O₂ (g) → 2 MgO (s)
S (s) + O₂ (g) → SO₂ (g)
2 HgO (s) $xrightarrow{heat}$ 2 Hg (l) + O₂ (g)
Mg (s) + S (s) → MgS (s)
Answer is Wrong!
Answer is Right!
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).