NEET ChemistryUpdated 19 Oct 2026

Redox Reactions: NEET PYQs and weightage

Redox Reactions carries 2.7 of 100 Chemistry marks in NEET by past-paper share: 19 of the 707 tagged NEET Chemistry PYQs in the ViJEEta bank (NEET 2013–2026). It ranks 20 of 26 Chemistry chapters.

Take the 25-question Redox Reactions test Formula sheet ↓All NEET Chemistry chapters

2.7/100 Weight in Chemistry

Exam importance (3/5, by past-paper share)

19 NEET PYQs

375 Practice questions

324 With measured difficulty

How the weight is computed: this chapter's tagged NEET PYQs divided by all tagged NEET Chemistry PYQs in the bank (19 of 707), times 100, with repeated questions counted once. The bank does not store the year of each NEET question, so none is printed. Computed from the bank at build time. Updated 19 Oct 2026.

Redox Reactions: formula sheet for NEET

14 formulas, each with when to use it. Copy it onto one page of your notebook: that page is this chapter's handbook.

Oxidation number sum rule
$\sum (oxidation numbers) = 0 (neutral compound)$
$\sum (oxidation numbers) = charge on the ion (polyatomic ion)$
$e.g. C O_{3}^{2 -} : x + 3 (- 2) = - 2 \to C = + 4$
Use it when: you need the oxidation number of one unknown atom in any formula or ion
Fixed oxidation numbers
$free element = 0 (H_{2}, O_{3}, P_{4}, S_{8}, Na)$
$monoatomic ion = its charge$
$alkali metals = + 1$
$alkaline earth metals = + 2$
$Al = + 3$
$F = - 1 (always)$
Use it when: you need known values to plug into the sum rule
Oxygen
$O = - 2 (normally)$
$- 1 (peroxides: H_{2} O_{2}, N a_{2} O_{2})$
$- \frac{1}{2} (superoxides: K O_{2}, Rb O_{2})$
$+ 2 (in O F_{2})$
$+ 1 (in O_{2} F_{2})$
Use it when: the compound has $O - O$ bonds or O bonded to F
Hydrogen
$H = + 1 (normally)$
$H = - 1 (binary metal hydrides: LiH, NaH, Ca H_{2})$
Use it when: H is bonded to a metal in a two-element compound
Highest oxidation number (representative elements)
$highest oxidation number = group number (groups 1, 2)$
$highest oxidation number = group number - 10 (groups 13 to 17)$
$Na + 1, Mg + 2, Al + 3, Si + 4, P + 5, S + 6, Cl + 7$
Use it when: deciding whether a species can still be oxidised, or can only act as an oxidant
Fractional oxidation number = average only
$C_{3} O_{2} \to \frac{4}{3} (really + 2, 0, + 2)$
$B r_{3} O_{8} \to \frac{16}{3} (really + 6, + 4, + 6)$
$S_{4} O_{6}^{2 -} \to 2.5 (really + 5, 0, 0, + 5)$
Use it when: the sum rule gives a fraction and the question asks for the actual states from the structure
Redox balance
$total increase in oxidation number = total decrease (electrons lost = electrons gained)$
Use it when: balancing by the oxidation number method; cross-multiply the per-formula changes
Half-reaction steps
Acidic: balance atoms other than O and H $\to$ add $H_{2} O$ for O $\to$ add $H^{+}$ for H $\to$ add $e^{-}$ for charge $\to$ equalise $e^{-}$ and add. Basic: add as many $O H^{-}$ as $H^{+}$ to both sides, then combine $H^{+} + O H^{-} \to H_{2} O$ .
Use it when: balancing any ionic redox equation, especially in basic medium
Permanganate, acidic
$Mn O_{4}^{-} + 8 H^{+} + 5 e^{-} \to M n^{2 +} + 4 H_{2} O (E^{\circ} = 1.51 V)$
Use it when: $KMn O_{4}$ in acidic medium (Mn $+ 7 \to + 2$ , 5 electrons)
Permanganate, basic
$Mn O_{4}^{-} + 2 H_{2} O + 3 e^{-} \to Mn O_{2} + 4O H^{-}$
Use it when: $KMn O_{4}$ in basic medium gives $Mn O_{2}$ (Mn $+ 7 \to + 4$ , 3 electrons)
Dichromate, acidic
$C r_{2} O_{7}^{2 -} + 14 H^{+} + 6 e^{-} \to 2C r^{3 +} + 7 H_{2} O (E^{\circ} = 1.33 V)$
$with F e^{2 +} : 6F e^{2 +} + C r_{2} O_{7}^{2 -} + 14 H^{+} \to 6F e^{3 +} + 2C r^{3 +} + 7 H_{2} O$
Use it when: $K_{2} C r_{2} O_{7}$ titrations (two Cr atoms, so 6 electrons, not 3)
Iodometry
$2C u^{2 +} + 4 I^{-} \to C u_{2} I_{2} + I_{2}$
$then I_{2} + 2 S_{2} O_{3}^{2 -} \to 2 I^{-} + S_{4} O_{6}^{2 -} (starch blue disappears at the end point)$
Use it when: an oxidant is estimated through the iodine it liberates (1 $I_{2}$ uses 2 $S_{2} O_{3}^{2 -}$ )
Disproportionation
$C l_{2} + 2O H^{-} \to Cl O^{-} + C l^{-} + H_{2} O (0 \to + 1 and - 1)$
$3Cl O^{-} \to 2C l^{-} + Cl O_{3}^{-}$
Use it when: the element sits in an intermediate state of at least three; $Cl O_{4}^{-}$ (Cl $+ 7$ ) and $F_{2}$ cannot disproportionate
Standard electrode potential
$E^{\circ} (H^{+} / H_{2}) = 0.00 V (298 K, 1 M, 1 atm)$
$more negative E^{\circ} = stronger reducing agent$
$more positive E^{\circ} = stronger oxidising agent (F_{2} / F^{-} + 2.87 V strongest oxidant, L i^{+} /Li - 3.05 V strongest reductant)$
Use it when: predicting which metal displaces which, or whether a redox reaction is feasible

Trap

Putting O = −2 in every compound. In peroxides (H₂O₂, Na₂O₂, CaO₂) it is −1, in superoxides (KO₂) it is −½, and with F it is positive. Look for O–O or O–F bonds before you use the sum rule.

How does NEET ask Redox Reactions?

8 real previous-year questions from this chapter, as printed in the paper, each with its worked solution. Answer the first one here with no sign-in.

Q1ChemistryNEET UG PYQTypes of Redox Reactions

Try right here · No sign-in

(I) H

_{2}

_{2}

+ O

_{3}

→ H

_{2}

O + 2O

_{2}

(II) H

_{2}

_{2}

+ Ag

_{2}

O → 2Ag + H

_{2}

O + O

_{2}

Role of hydrogen peroxide in the above reactions is respectively:

Answer key (A) & worked solution

Correct answer: Option A

_{2}

_{2}

+ O

_{3}

→ H

_{2}

O + 2O

_{2}

_{2}

_{2}

is oxidised to O

_{2}

. Hence, it acts as reducing agent.

H_{2} O_{2} + A g_{2} + 1 O^{- 2} Reduction 2 A 0 g + H_{2} O + O_{2}

Q2ChemistryNEET UG PYQConcept of Oxidation and Reduction

Which of the following processes does not involve oxidation of iron?

ALiberation of H

_{2}

from steam by iron at high temperature

BRusting of iron sheets

CDecolourization of blue CuSO

_{4}

solution by iron.

DFormation of Fe(CO)

_{5}

from Fe.

Answer key (D) & worked solution

Correct answer: Option D

In metal carbonyl complexes, metal exhibit zero oxidation state.

Q3ChemistryNEET UG PYQTypes of Redox Reactions

The pair of compounds that can exist together is

AFeCl

_{2}

, SnCl

_{2}

BFeCl

_{3}

, Kl

CFeCl

_{3}

, SnCl

_{2}

DHgCl

_{2}

, SnCl

_{2}

Answer key (A) & worked solution

Correct answer: Option A

FeCl

_{2}

+ SnCl

_{2}

→ No reaction FeCl

_{3}

+ KI → K[FeCl

_{3}

I] FeCl

_{3}

+ SnCl

_{2}

→ FeCl

_{2}

+ SnCl

_{4}

HgCl

_{2}

+ SnCl

_{2}

→ Hg + SnCl

_{4}

In option (a) , no reaction is taking place, means they can exist together.

Q4ChemistryNEET UG PYQOxidation Number

The correct decreasing order of oxidation state of the underlined atom in each molecule is

\underline{N}_{2} O_{5} > \underline{Al}_{2} O_{3} > H_{2} \underline{S}

\underline{PbO}_{2} > \underline{N}_{2} O_{3} > \underline{SO}_{3}

\underline{P}_{4} O_{6} > \underline{Cl}_{2} O_{7} > \underline{AlH} H_{3}

\underline{P}_{4} O_{10} > \underline{SO} O_{3} > H_{2} \underline{O}

Answer key (A) & worked solution

Correct answer: Option A

P 4^{+ 3} O_{6}, + C I_{2}^{O_{7}}, Al + 3 H_{3}

\underline{P}_{4} O_{10}, \underline{SO}_{3}^{+ 6}, H_{2} \underline{- 2} \underline{N}_{2}^{+ 5} O_{5}, \underline{Al_{2}^{+ 3}} O_{3}, H_{2} \underline{- 2} \underline{+ 4} \underline{Pb_{2}}, \underline{N}_{2}^{+ 3} O_{3}, \underline{+ 6} O_{3}

Q5ChemistryNEET UG PYQRedox Titrations

Name the gas that can readily decolourise acidified KMnO

_{4}

solution

ANO

_{2}

_{2}

_{5}

CCO

_{2}

DSO

_{2}

Answer key (D) & worked solution

Correct answer: Option D

_{2}

is readily decolourises acidified KMnO

_{4}

.KMnO

_{4}

is an oxidizing agent, while SO

_{2}

is a reducing agent. When SO

_{2}

comes into contact with an acidified KMnO

_{4}

solution, the KMnO

_{4}

is decolorized.

Q6ChemistryNEET UG PYQRedox Titrations

The reaction of aqueous KMnO

_{4}

with H

_{2}

_{2}

in acidic condition gives

AMn

^{2 +}

and O

_{3}

BMn

^{4 +}

and MnO

_{2}

CMn

^{4 +}

and O

_{2}

DMn

^{2 +}

and O

_{2}

Answer key (D) & worked solution

Correct answer: Option D

2KMnO

_{4}

+ 3H

_{2}

_{4}

+ 5H

_{2}

_{2}

↓ K

_{2}

_{4}

+ 2MnSO

_{4}

+ 5H

_{2}

O + 5O

_{2}

Q7ChemistryNEET UG PYQOxidation Number

The correct order of N-compounds in its decreasing order of oxidation states is

AHNO

_{3}

, NH

_{4}

Cl, NO, N

BHNO

_{3}

, NO, NH

_{4}

Cl, N

CHNO

_{3}

, NO, N

_{2}

, NH

_{4}

DNH

_{4}

Cl, N

_{2}

, NO, HNO

_{3}

Answer key (C) & worked solution

Correct answer: Option C

H N + 5 O_{3}, N + 2 O, N O_{2}, N - 3 H_{4} C l

Q8ChemistryNEET UG PYQTypes of Redox Reactions

Which one of the following statement is correct when SO

_{2}

is passed through acidified K

_{2}

_{2}

_{7}

solution?

AGreen Cr

_{2}

(SO

_{4}

)

_{3}

is formed

BThe solution turns blue

CThe solution is decolourized

DSO

_{2}

is reduced

Answer key (A) & worked solution

Correct answer: Option A

_{2}

_{2}

_{7}

→ Cr

_{2}

(SO

_{4}

)

_{3}

green solution obtain whereas SO

_{2}

oxidises into sulphate

S O_{4}^{2 -}

_{2}

_{2}

_{7}

+ SO

_{2}

+ H

_{2}

_{4}

→ Cr

_{2}

(SO

_{4}

)

_{3}

+ H

_{2}

O + K

_{2}

_{4}

)

Which topics in Redox Reactions carry the most questions?

All 9 topics, by tagged PYQs, then practice questions. Counted from the bank. Updated 19 Oct 2026.

Topic	PYQs	Practice questions
Types of Redox Reactions	7	96
Oxidation Number	6	102
Redox Titrations	3	50
Balancing Redox Reactions	2	41
Concept of Oxidation and Reduction	1	18
Equivalent Concept	0	40
Volume Strength of Hydrogen Peroxide	0	17
Introduction to Redox Reactions	0	7
Redox Reactions and Electrode Processes	0	4

Why does Redox Reactions show "–" until you answer 3 questions?

Unknown is not zero. Until you answer at least 3 graded questions in Redox Reactions, ViJEEta shows – instead of a zero or a 50% default. Book exercises can raise chapter mastery up to 0.60, adaptive practice up to 0.75, and only a timed chapter test or mock can certify 0.80 and above.

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What happens when you test Redox Reactions?

Every chapter test is 25 questions. It starts at moderate difficulty and adapts after each saved answer. If you open a solution before answering, that attempt earns no credit, so your mastery stays honest.

Start the Redox Reactions test

Chapters either side of Redox Reactions by weight

Organic Chemistry: Some Basic Principles and Techniques Weight 3.0/100 Chemical Equilibrium Weight 2.8/100 p-Block Elements (Group 13 and 14) Weight 2.7/100 Practical Chemistry Weight 2.5/100

Redox Reactions: NEET PYQs and weightage

Redox Reactions: formula sheet for NEET

Oxidation number sum rule

Fixed oxidation numbers

Oxygen

Hydrogen

Highest oxidation number (representative elements)

Fractional oxidation number = average only

Redox balance

Half-reaction steps

Permanganate, acidic

Permanganate, basic

Dichromate, acidic

Iodometry

Disproportionation

Standard electrode potential

How does NEET ask Redox Reactions?

Which topics in Redox Reactions carry the most questions?

Why does Redox Reactions show "–" until you answer 3 questions?

What happens when you test Redox Reactions?

Chapters either side of Redox Reactions by weight