{"id":87360,"date":"2025-06-01T06:41:39","date_gmt":"2025-06-01T06:41:39","guid":{"rendered":"https:\/\/exam.pscnotes.com\/mcq\/?p=87360"},"modified":"2025-06-01T06:41:39","modified_gmt":"2025-06-01T06:41:39","slug":"which-one-of-the-following-is-a-reduction-reaction","status":"publish","type":"post","link":"https:\/\/exam.pscnotes.com\/mcq\/which-one-of-the-following-is-a-reduction-reaction\/","title":{"rendered":"Which one of the following is a reduction reaction?"},"content":{"rendered":"

Which one of the following is a reduction reaction?<\/p>\n

[amp_mcq option1=”2 Mg (s) + O\u2082 (g) \u2192 2 MgO (s)” option2=”S (s) + O\u2082 (g) \u2192 SO\u2082 (g)” option3=”2 HgO (s) $\\xrightarrow{heat}$ 2 Hg (l) + O\u2082 (g)” option4=”Mg (s) + S (s) \u2192 MgS (s)” correct=”option3″]<\/p>\n

\n
\n
This question was previously asked in<\/div>\n
UPSC NDA-1 – 2016<\/div>\n<\/div>\n
Download PDF<\/a>Attempt Online<\/a><\/div>\n<\/div>\n
\nThe correct answer is C) 2 HgO (s) $\\xrightarrow{heat}$ 2 Hg (l) + O\u2082 (g).
\n<\/section>\n
\nReduction 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.
\n<\/section>\n
\nLet’s look at the other options:
\nA) 2 Mg (s) + O\u2082 (g) \u2192 2 MgO (s): Mg is oxidized (0 to +2), O\u2082 is reduced (0 to -2).
\nB) S (s) + O\u2082 (g) \u2192 SO\u2082 (g): S is oxidized (0 to +4), O\u2082 is reduced (0 to -2).
\nD) Mg (s) + S (s) \u2192 MgS (s): Mg is oxidized (0 to +2), S is reduced (0 to -2).
\nAll listed reactions are redox reactions involving both oxidation and reduction. However, option C specifically shows the reduction of a metal cation (Hg\u00b2\u207a) to its elemental form (Hg\u2070) 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).
\n<\/section>\n","protected":false},"excerpt":{"rendered":"

Which one of the following is a reduction reaction? [amp_mcq option1=”2 Mg (s) + O\u2082 (g) \u2192 2 MgO (s)” option2=”S (s) + O\u2082 (g) \u2192 SO\u2082 (g)” option3=”2 HgO (s) $\\xrightarrow{heat}$ 2 Hg (l) + O\u2082 (g)” option4=”Mg (s) + S (s) \u2192 MgS (s)” correct=”option3″] This question was previously asked in UPSC NDA-1 … <\/p>\n

Detailed SolutionWhich one of the following is a reduction reaction?<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1093],"tags":[1098,1096,1155],"class_list":["post-87360","post","type-post","status-publish","format-standard","hentry","category-upsc-nda-1","tag-1098","tag-chemistry","tag-physical-and-chemical-changes-solution","no-featured-image-padding"],"yoast_head":"\nWhich one of the following is a reduction reaction?<\/title>\n<meta name=\"description\" content=\"The correct answer is C) 2 HgO (s) $xrightarrow{heat}$ 2 Hg (l) + O\u2082 (g). 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.\" \/>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/exam.pscnotes.com\/mcq\/which-one-of-the-following-is-a-reduction-reaction\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Which one of the following is a reduction reaction?\" \/>\n<meta property=\"og:description\" content=\"The correct answer is C) 2 HgO (s) $xrightarrow{heat}$ 2 Hg (l) + O\u2082 (g). 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.\" \/>\n<meta property=\"og:url\" content=\"https:\/\/exam.pscnotes.com\/mcq\/which-one-of-the-following-is-a-reduction-reaction\/\" \/>\n<meta property=\"og:site_name\" content=\"MCQ and Quiz for Exams\" \/>\n<meta property=\"article:published_time\" content=\"2025-06-01T06:41:39+00:00\" \/>\n<meta name=\"author\" content=\"rawan239\" \/>\n<meta name=\"twitter:card\" content=\"summary_large_image\" \/>\n<meta name=\"twitter:label1\" content=\"Written by\" \/>\n\t<meta name=\"twitter:data1\" content=\"rawan239\" \/>\n\t<meta name=\"twitter:label2\" content=\"Est. reading time\" \/>\n\t<meta name=\"twitter:data2\" content=\"1 minute\" \/>\n<!-- \/ Yoast SEO Premium plugin. -->","yoast_head_json":{"title":"Which one of the following is a reduction reaction?","description":"The correct answer is C) 2 HgO (s) $xrightarrow{heat}$ 2 Hg (l) + O\u2082 (g). 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.","robots":{"index":"index","follow":"follow","max-snippet":"max-snippet:-1","max-image-preview":"max-image-preview:large","max-video-preview":"max-video-preview:-1"},"canonical":"https:\/\/exam.pscnotes.com\/mcq\/which-one-of-the-following-is-a-reduction-reaction\/","og_locale":"en_US","og_type":"article","og_title":"Which one of the following is a reduction reaction?","og_description":"The correct answer is C) 2 HgO (s) $xrightarrow{heat}$ 2 Hg (l) + O\u2082 (g). 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.","og_url":"https:\/\/exam.pscnotes.com\/mcq\/which-one-of-the-following-is-a-reduction-reaction\/","og_site_name":"MCQ and Quiz for Exams","article_published_time":"2025-06-01T06:41:39+00:00","author":"rawan239","twitter_card":"summary_large_image","twitter_misc":{"Written by":"rawan239","Est. reading time":"1 minute"},"schema":{"@context":"https:\/\/schema.org","@graph":[{"@type":"WebPage","@id":"https:\/\/exam.pscnotes.com\/mcq\/which-one-of-the-following-is-a-reduction-reaction\/","url":"https:\/\/exam.pscnotes.com\/mcq\/which-one-of-the-following-is-a-reduction-reaction\/","name":"Which one of the following is a reduction reaction?","isPartOf":{"@id":"https:\/\/exam.pscnotes.com\/mcq\/#website"},"datePublished":"2025-06-01T06:41:39+00:00","dateModified":"2025-06-01T06:41:39+00:00","author":{"@id":"https:\/\/exam.pscnotes.com\/mcq\/#\/schema\/person\/5807dafeb27d2ec82344d6cbd6c3d209"},"description":"The correct answer is C) 2 HgO (s) $\\xrightarrow{heat}$ 2 Hg (l) + O\u2082 (g). 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. 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