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NEET Redox Reactions: 5 practice MCQs with answers

By the PrepMatic team · Updated 9 Oct 2026 · 3 min read

Redox Reactions is a short Class 11 chapter whose skills, assigning oxidation numbers and spotting oxidising and reducing agents, are reused in electrochemistry, the p-block, the d-block and organic chemistry. The five MCQs below cover oxidation numbers, disproportionation, the n-factor of KMnO₄ and the oxidation state of carbon.

What this chapter covers in the NEET syllabus

The NMC combines Redox Reactions and Electrochemistry into one unit. This page covers the redox half, taught as the NCERT Class 11 chapter Redox Reactions, and the electrochemistry half is on NEET Electrochemistry. The topics are:

• Oxidation and reduction as electron transfer, and as changes in oxidation number.
• Rules for assigning oxidation numbers.
• Oxidising and reducing agents, and types of redox reactions: combination, decomposition, displacement and disproportionation.
• Balancing redox equations by the oxidation number method and the half-reaction (ion-electron) method.

Five practice MCQs on Redox Reactions

Question 1

The oxidation number of chromium in K₂Cr₂O₇ is:

• A. +3
• B. +6
• C. +7
• D. +12

Question 2

The oxidation number of oxygen in hydrogen peroxide, H₂O₂, is:

• A. −2
• B. 0
• C. +1
• D. −1

Question 3

Which of the following is an example of a disproportionation reaction?

• A. 2Na + Cl₂ → 2NaCl
• B. N₂ + O₂ → 2NO
• C. 2H₂O₂ → 2H₂O + O₂
• D. Zn + CuSO₄ → ZnSO₄ + Cu

Question 4

How many electrons does one MnO₄⁻ ion gain when it is reduced to Mn²⁺ in acidic medium?

• A. 5
• B. 3
• C. 1
• D. 7

Question 5

The oxidation number of carbon in formaldehyde, HCHO, is:

• A. +2
• B. −2
• C. +4
• D. 0

Answers and explanations

1. B. The sum of oxidation numbers in a neutral compound is zero. Two K contribute +2, seven O contribute −14, so 2 × (Cr) = +12 and Cr = +6.
2. D. In peroxides, oxygen is in the −1 state because the O-O bond is homonuclear. This is why H₂O₂ can act as both an oxidising agent (−1 to −2) and a reducing agent (−1 to 0).
3. C. In 2H₂O₂ → 2H₂O + O₂, oxygen goes from −1 to −2 (in water) and to 0 (in O₂), so the same element is both reduced and oxidised. In the other reactions, different elements are oxidised and reduced.
4. A. In acidic medium MnO₄⁻ is reduced to Mn²⁺: Mn goes from +7 to +2, a gain of 5 electrons. This number is the n-factor of KMnO₄ in acid. In neutral medium (MnO₂) it is 3, and in strongly alkaline medium (MnO₄²⁻) it is 1.
5. D. For HCHO: 2(+1) + x + (−2) = 0, so x = 0. Carbon moves through −4 (CH₄), −2 (CH₃OH), 0 (HCHO), +2 (HCOOH) and +4 (CO₂) as it is oxidised.

How to prepare Redox Reactions

• Memorise the oxidation number rules with their exceptions. Hydrogen is +1 (−1 in metal hydrides), oxygen is −2 (−1 in peroxides, +2 in OF₂, −½ in superoxides), and fluorine is always −1. The sum of oxidation numbers equals the charge on the species.
• Practise unusual cases. Average oxidation numbers appear in Fe₃O₄, S₄O₆²⁻ and Na₂S₂O₃. Learn to spot that the same element can have two different oxidation numbers in one compound.
• Identify the oxidising agent as the species that is reduced, and the reducing agent as the species that is oxidised. Many students reverse these under pressure. Writing "OIL RIG" (oxidation is loss, reduction is gain) in the margin of your notes helps.
• Balance by the ion-electron method in acid and base. Balance atoms other than H and O, then O with H₂O, then H with H⁺ (add OH⁻ for basic medium), then balance charge with electrons.
• Use the n-factor for titration problems. This idea goes a little beyond the NCERT text but is widely used. Equivalents of oxidising agent equal equivalents of reducing agent. Know the n-factors of KMnO₄, K₂Cr₂O₇ (6), oxalic acid (2) and Fe²⁺ (1).

A week of ten problems a day, mixing oxidation numbers, balancing and n-factor questions, makes this chapter automatic. See the NEET Chemistry preparation guide for the wider plan and the NEET syllabus for the unit list.

Take a full Redox Reactions test on PrepMatic

Redox is a chapter you can revise in a few days and test straight away. A PrepMatic topic test (about 15 questions in 30 minutes) is scored with NEET's negative marking and is part of the free Basic plan. Continue with Electrochemistry or browse the practice hub.

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