How do you find the oxidation state of an element in a compound?

Use these rules in order: (1) Free elements have oxidation state 0. (2) Monatomic ions have OS = their charge. (3) In compounds, F is always −1. (4) O is usually −2 (except in peroxides: −1, in OF₂: +2). (5) H is +1 with non-metals and −1 with metals. (6) The sum of all oxidation states equals the charge of the species (0 for neutral molecules, equal to ionic charge for ions). Apply these rules and solve for the unknown element.

What is the difference between an oxidising agent and a reducing agent?

An oxidising agent (oxidant) accepts electrons — it gets reduced (its oxidation state decreases). A reducing agent (reductant) donates electrons — it gets oxidised (its oxidation state increases). A useful memory trick: OIL RIG — Oxidation Is Loss (of electrons), Reduction Is Gain (of electrons).

What is a disproportionation reaction?

A disproportionation reaction is one in which the same element is simultaneously oxidised and reduced. For example, in 2H₂O₂ → 2H₂O + O₂, oxygen goes from −1 (in H₂O₂) to −2 (in H₂O) and also to 0 (in O₂). So oxygen is both oxidised and reduced.

What is the ion-electron method for balancing redox equations?

Split the reaction into two half-reactions: one for oxidation and one for reduction. Balance each half-reaction separately (balance atoms, then add H₂O for O, H⁺ for H in acidic media, or OH⁻/H₂O in basic media, then add electrons to balance charge). Multiply the half-reactions to equalise electrons, then add them together and cancel common terms.

What is the electrochemical series and why is it useful?

The electrochemical series (electromotive series) is a list of elements (and their ions) arranged in order of their standard reduction potential (E°). Elements higher in the series (more positive E°) are better oxidising agents. Elements lower in the series (more negative E°) are better reducing agents. A metal can displace another metal from its salt solution only if it is above the other metal in the activity series (lower reduction potential).

How is a galvanic cell different from an electrolytic cell?

A galvanic (voltaic) cell converts chemical energy into electrical energy spontaneously (ΔG 0). In electrolytic cells, the anode is connected to the positive terminal of the battery.

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Chemistry

Redox Reactions

Redox ReactionsNEET Chemistry · Class 11 · NCERT Chapter 7

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All (8)

Redox Reactions (8)

Fe(NO2)2

FeSO4

FeSO3

Solution

MnO4 −⟶Mn2+ ; Change in oxidation no. = 5 In option, i. Fe2+ ⟶Fe3+ Change in oxidation no. = 1 ii. Fe2+ ⟶Fe3+ Change in oxidation no. = 1 SO3 2−⟶SO4 2− Change in oxidation no. = 2 =1+2=3 iii. Fe2+ ⟶Fe3+ Change in oxidation no. = 1 C2O4 2−⟶2CO2 Change in oxidation no. = 2 =1+2=3 iv. Fe2+ ⟶Fe3+ Change in oxidation no. = 1 2NO2 −⟶2NO3 − Change in oxidation no. = 4 =1+4=5

The solution turns blue.

The solution is decolourized.

SO2 is reduced.

Green Cr2(SO4)3 is formed.

Solution

K2Cr2O7 + SO2 + H2SO4 → K 2SO4 + Cr 2(SO4)3 + Green H2O www.vedantu.com 34

HNO 3 , NH 4 Cl, NO, N 2

HNO 3 , NO, NH 4 Cl, N 2

HNO 3 , NO, N 2 , NH 4 Cl

NH 4 Cl, N 2 , NO, HNO 3

Solution

The oxidation states of nitrogen in the given compounds are: $HNO_{3}$ (+5), $NO$ (+2), $NH_{4} Cl$ (-3), and $N_{2}$ (0). Therefore, the correct order in decreasing oxidation states is $HNO_{3}$ , $NO$ , $NH_{4} Cl$ , $N_{2}$ , so option (b) is correct.

2 16 5

2 5 16

16 5 2

5 16 2

Solution

The balanced redox reaction is $2 MnO_{4}^{-} + 5 C_{2} O_{4}^{2 -} + 16 H^{+} \to 2 Mn^{2 +} + 10 CO_{2} + 8 H_{2} O$ . The correct coefficients for the reactants are 2 for $MnO_{4}^{-}$ , 5 for $C_{2} O_{4}^{2 -}$ , and 16 for $H^{+}$ , so option (b) is correct.

H3C−CH | Cl − CH3 | CH | CH3

Cl−CH2−CH2− CH3 | CH | CH3

H3C−CH2− CH2Cl | CH−CH3

H3C−CH2− CH3 | C−CH3 | Cl

Solution

CH3−C= | CH3 CH−CH3 A HCl → H3C−CH3− CH3 | C−CH3 | Cl

+ 4 to + 4

0 to + 4

− 4 to + 4

0 to − 4

Solution

In $CH_{4}$ , the oxidation number of carbon is $- 4$ (since hydrogen is $+ 1$ ). In $CCl_{4}$ , the oxidation number of carbon is $+ 4$ (since chlorine is $- 1$ ). Thus, the change in oxidation number of carbon is from $- 4$ to $+ 4$ , so option (c) is correct.

Zn + CuSO4 → ZnSO4 + Cu

2KClO3 + I2 → 2KIO3 + Cl2

H2 + Cl2 → 2HCl

BaCl2 + Na2SO4 → BaSO4 + 2NaCl

Solution

(1) (2) (3) (4) 2 1 2 11 2 1 2 2 4 4BaCl Na SO BaSO 2NaCl + + + +− − −+ ⎯⎯ → + This is not a redox reaction as there is no change in oxidation state.

+1, -1, and +6

+2, -2, and +6

+1, -2, and +4

+4, -4, and +6

Solution

KO₂: Alkali metal K always shows +1 oxidation state, so K is +1.

H₂O₂: H is +1, total H contribution = +2. The molecule is neutral, so O₂ must total −2. With two equivalent peroxide oxygens, oxidation state of O is −1 each.

H₂SO₄: H is +1 (×2 = +2), each O is −2 (×4 = −8). Sulphur balances the rest: S + 2 − 8 = 0, so S = +6.

Oxidation states are: K = +1, O (in H₂O₂) = −1, S = +6.

Hence option (1): +1, −1, +6.

Redox ReactionsNEET Chemistry · Class 11 · NCERT Chapter 7

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Redox ReactionsNEET Chemistry · Class 11 · NCERT Chapter 7

1NEET 2015Medium4 bookletsAssuming complete ionization, same moles of which of the following compounds will require the least amount of acidified KMnO4 for complete oxidation? www.vedantu.com 55

2NEET 2016Medium4 bookletsWhich one of the following statements is correct when SO2 is passed through acidified K2Cr2O7 solution?

3NEET 2018Medium20 bookletsThe correct order of N-compounds in its decreasing order of oxidation states is

4NEET 2018Medium20 bookletsFor the redox reaction Mn – 4 O + C 2 – 2 4 O + H + ⎯→ ⎯ Mn 2+ + CO 2 + H 2 O the correct coefficients of the reactants for the balanced equation are Mn – 4 O – 2 4 2 O C H +

5NEET 2019Medium4 bookletsAn alkene “A” on reaction with 𝑂3 and Zn – 𝐻2𝑂 gives propanone and ethanal in equimolar ratio. Addition of HCl to alkene “A” gives “B” as the major product. The structure of product “B” is:

6NEET 2020Medium24 bookletsWhat is the change in oxidation number of carbon in the following reaction ? CH 4 (g) + 4Cl 2 (g) → CCl 4 (l) + 4HCl(g)

7NEET 2024Medium24 bookletsWhich reaction is NOT a redox reaction?

8NEET 2025Medium4 bookletsConsider the following compounds : K​O2​, H2​O​2​ and H2​S​O4​ The oxidation state of the underlined elements in them are, respectively,

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