Reduction is a chemical process that involves the gain of electrons, a decrease in oxidation state, gain of hydrogen, or loss of oxygen. In option C, Mercury (Hg) in mercuric oxide (HgO) has an oxidation state of +2. In the product, elemental mercury (Hg) has an oxidation state of 0. The oxidation state of Hg decreases from +2 to 0, which signifies a reduction. Also, the metal oxide is losing oxygen to form the metal, which is a characteristic of reduction processes.
Which one of the following is a reduction reaction?
Asked in UPSC NDA 1 2016 · UPSC NDA 2 2018 · Topic: Physical and Chemical Changes, Solution (Definition and Characteristics of Chemical Changes (Chemical Reactions))
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Answer: C. 2 HgO (s) $\xrightarrow{heat}$ 2 Hg (l) + O₂ (g)
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