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Change in oxidation number of an element in a given reaction or conversion

This type of question, asked 6 times: 10 May 2023 S2, 15 May 2023 S2, 12 May 2024 S2, 22 Apr 2025 S1, 19 Apr 2026 S1, 20 Apr 2026 S1. All 6 questions below, oldest first.

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  1. Question 1

    10 May 2023 S2

    95
    What is the change in oxidation number of S in following reaction? H2S+NO3−→H2O+NO+S\text{H}_2\text{S} + \text{NO}_3^- \rightarrow \text{H}_2\text{O} + \text{NO} + \text{S}

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  2. Question 2

    15 May 2023 S2

    88
    What is change in oxidation number of nitrogen when NO3−\text{NO}_3^- is converted to NH4+\text{NH}_4^+ ion?

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  3. Question 3

    12 May 2024 S2

    52
    What is the change in oxidation number of Cr in the following redox reaction? 3H2O2(aq)+Cr2O72−(aq)+8H+(aq)→3O2(g)+2Cr3++7H2O3H_2O_2(aq) + Cr_2O_7^{2-}(aq) + 8H^+(aq) \rightarrow 3O_2(g) + 2Cr^{3+} + 7H_2O

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  4. Question 4

    22 Apr 2025 S1

    57
    What is the difference in oxidation number of Mn in KMnO4KMnO_{4} and MnO2MnO_{2} ?

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  5. Question 5

    19 Apr 2026 S1

    13
    Identify change in oxidation state of oxidising agent in following redox reaction. 3H3AsO3(aq)+BrO3(aq)−⟶Br(aq)−+3H3AsO4(aq)\mathrm{3H_3AsO_{3(aq)} + BrO^-_{3(aq)} \longrightarrow Br^-_{(aq)} + 3H_3AsO_{4(aq)}}

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  6. Question 6

    20 Apr 2026 S1

    12
    What is the difference in oxidation number of nitrogen when nitric acid is converted into nitrous oxide ?

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