Chemistry · chapter PYQs

Redox Reactions, on the exam screen.

3 questions from Re-NEET 2026, NEET 2020, 3 minutes, marked +4 / −1. See them with solutions.

Redox Reactions · PYQs

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Question 1 · Re-NEET 2026 · Q57 · +4 / −1
In an acidic medium, 10 mL of 0.25 M oxalic acid is titrated with $\mathrm{KMnO}_{4}$ solution. If the volume of $\mathrm{KMnO}_{4}$ solution required to reach end point is 10 mL, the strength of the $\mathrm{KMnO}_{4}$ solution is
Answer and explanation
Answer: (1)
Oxalate is oxidised by two electrons ( $\mathrm{C}_{2}\mathrm{O}_{4}^{2-} \rightarrow 2\mathrm{CO}_{2} + 2\mathrm{e}^{-}$ ) so its n-factor is 2, while permanganate in ACIDIC medium is reduced by five electrons ( $\mathrm{MnO}_{4}^{-} \rightarrow \mathrm{Mn}^{2+}$ ) so its n-factor is 5. Equating equivalents, $(0.25 \times 2)(10) = (M \times 5)(10)$ , giving $M = 0.10\ \text{M}$ . NCERT Class 11, Redox Reactions (redox titrations).
Question 2 · Re-NEET 2026 · Q81 · +4 / −1
The correct decreasing order of oxidation state of the underlined atom in each molecule is
Answer and explanation
Answer: (2)
Assigning oxidation numbers in option (2): nitrogen in $\mathrm{N}_{2}\mathrm{O}_{5}$ is +5, aluminium in $\mathrm{Al}_{2}\mathrm{O}_{3}$ is +3, and sulphur in $\mathrm{H}_{2}\mathrm{S}$ is -2 (hydrogen is +1 because sulphur is the more electronegative partner). The sequence +5 > +3 > -2 is genuinely decreasing, so (2) is correct. NCERT Class 11, Redox Reactions (oxidation number rules).
Question 3 · NEET 2020 · Q131 · +4 / −1
What is the change in oxidation number of carbon in the reaction CH $_{4}$ (g) + 4Cl $_{2}$ (g) → CCl $_{4}$ (l) + 4HCl(g)?
Answer and explanation
Answer: (2)
In $\mathrm{CH}_{4}$ , the oxidation number of carbon is -4 (since hydrogen is +1). In $\mathrm{CCl}_{4}$ , the oxidation number of carbon is +4 (since chlorine is -1). Thus, the change in oxidation number of carbon is from -4 to +4. Chapter: Redox Reactions.