How much of JEE Main comes from Redox Reactions and Electrochemistry?

JEEGenie estimates about 5% of JEE Main marks come from Redox Reactions and Electrochemistry, based on recent papers. The share varies from year to year.

Which formulas matter most in Redox Reactions and Electrochemistry?

The Redox Reactions and Electrochemistry sheet on this page has 12 formula entries, starting with Standard Electrode Potential (E°), Nernst Equation, Gibbs Free Energy and Cell Potential, Equilibrium Constant from E°, Faraday's Laws of Electrolysis. Each one comes with when to use it and the trap to avoid.

What topics does Redox Reactions and Electrochemistry cover for JEE?

Redox Reactions and Electrochemistry covers Oxidation Number, Balancing Redox Reactions, Electrochemical Cells, Nernst Equation, Electrolysis, Conductance.

How should I revise Redox Reactions and Electrochemistry before the exam?

Learn each formula together with its condition of use, read the trap listed beside it, then practise questions and review every mistake. The practice link on this page opens Redox Reactions and Electrochemistry questions on JEEGenie.

How many previous-year questions are there on Redox Reactions and Electrochemistry?

JEEGenie has 501 previous-year questions on Redox Reactions and Electrochemistry, and this page shows a few with worked explanations.

Is practice on Redox Reactions and Electrochemistry free on JEEGenie?

Sign-up is free and includes a 7-day Pro trial. After the trial, free accounts keep a limited daily quota.

Redox Reactions and Electrochemistry for JEE Main & Advanced — formulas, what is asked, and traps

JEEGenie estimates about 5% of JEE Main marks come from Redox Reactions and Electrochemistry. This page covers 12 formula entries, each with when to use it, what JEE asks and the traps. A common slip: Confusing oxidation with addition of oxygen only; remember it's about electron transfer.

Key points to know

Oxidation and Reduction. Oxidation is loss of electrons (increase in oxidation number), reduction is gain of electrons (decrease in oxidation number).
Oxidizing and Reducing Agents. Oxidizing agent (oxidant) gains electrons and gets reduced; reducing agent (reductant) loses electrons and gets oxidized.
Electrochemical Cell. A device that converts chemical energy to electrical (galvanic/voltaic) or vice versa (electrolytic). Redox reactions occur at electrodes.
Electrochemical Series. A list of standard electrode potentials in increasing order. Top (most negative) are strong reductants; bottom (most positive) are strong oxidants.
Conductance in Electrolytes. Molar conductivity ( $Λ_{m}$ ) = $\frac{κ}{C}$ , where $κ$ is conductivity. It increases with dilution for weak electrolytes due to increased dissociation.
Electrolytic Cells and Electrolysis. In electrolytic cells, external voltage drives non-spontaneous redox reactions. Anode is positive, cathode negative.
Batteries and Fuel Cells. Primary batteries (non-rechargeable, e.g., dry cell), secondary (rechargeable, e.g., lead-acid), fuel cells (continuous fuel supply, e.g., H2-O2 cell).
Corrosion. Electrochemical oxidation of metals, e.g., rusting of iron: Fe oxidized at anode, O2 reduced at cathode. Presence of water and electrolyte accelerates.
Standard Hydrogen Electrode (SHE). Reference electrode with E° = 0 V at all temperatures. Consists of Pt electrode in 1 M H⁺ with H2 gas at 1 atm.
Concentration Cells. Cell with same electrodes but different ion concentrations. Ecell = (0.0591/n) log(C2/C1) where C2 > C1 at cathode.

Formula sheet

Name	Formula	When to use
Standard Electrode Potential (E°)	$E_{cell}^{\circ} = E_{cathode}^{\circ} - E_{anode}^{\circ}$	Calculate cell potential and predict spontaneity.
Nernst Equation	$E = E^{\circ} - \frac{R T}{n F} \ln Q$	Calculate cell potential under non-standard conditions or equilibrium constant.
Gibbs Free Energy and Cell Potential	$Δ G = - n F E_{cell}$	Relate electrochemical data to thermodynamics.
Equilibrium Constant from E°	$E^{\circ} = \frac{0.0591}{n} \log K$	Calculate equilibrium constant from standard cell potential.
Faraday's Laws of Electrolysis	$m = \frac{I t M}{n F}$	Calculate mass, time, or current in electrolysis.
Conductance in Electrolytes	$Λ_{m} = \frac{κ}{C}$	Study electrolyte behavior and determine degree of dissociation.
Kohlrausch's Law	$Λ_{m}^{\infty} = \sum ν_{i} λ_{i}^{\infty}$	Calculate Λm° for weak electrolytes or find degree of dissociation.
Degree of Dissociation (α) from Conductivity	$α = \frac{Λ_{m}}{Λ_{m}^{\infty}}$	Determine dissociation constant of weak acids/bases from conductivity data.
Relation Between ΔG°, E°, and K	$Δ G^{\circ} = - n F E^{\circ} = - R T \ln K$	Convert between thermodynamic and electrochemical quantities.
Disproportionation Reactions	$E_{cell}^{\circ} = E_{reduction}^{\circ} - E_{oxidation}^{\circ}$	Predict if a species (e.g., Cu+, MnO4²⁻) undergoes disproportionation.
Standard Hydrogen Electrode (SHE)	$2 H^{+} + 2 e^{-} \to H_{2}$	Measure electrode potentials relative to SHE.
Concentration Cells	$E_{cell} = \frac{0.0591}{n} \log \frac{C_{cathode}}{C_{anode}}$	Calculate potential due to concentration difference.

Open the Redox Reactions and Electrochemistry formula page

What JEE asks

Oxidation and Reduction. JEE often asks to classify reactions as redox or not, or to identify the species oxidized/reduced.
Oxidation Number Rules. JEE frequently tests oxidation number of elements in unusual compounds (e.g., Fe in Fe3O4, S in H2S2O8).
Oxidizing and Reducing Agents. JEE often asks to identify the strongest oxidizing/reducing agent from a list or from standard potentials.
Balancing Redox Reactions (Half-Reaction Method). JEE often gives unbalanced redox equations in acidic/basic medium and asks for coefficients or balanced equation.
Electrochemical Cell. JEE asks to identify anode/cathode, direction of electron flow, or cell representation.
Standard Electrode Potential (E°). JEE often gives standard potentials and asks for E°cell or to compare oxidizing power.
Nernst Equation. JEE frequently asks to find Ecell given concentrations, or to find concentration from Ecell.
Gibbs Free Energy and Cell Potential. JEE asks to calculate ΔG from E° or vice versa, or to predict spontaneity.
Equilibrium Constant from E°. JEE often asks to find K from E° or vice versa, especially for solubility or complexation.
Electrochemical Series. JEE asks to predict if a metal can displace another from its salt, or to arrange in order of reducing power.
Faraday's Laws of Electrolysis. JEE often gives current and time to find mass deposited, or vice versa, sometimes with series cells.
Conductance in Electrolytes. JEE asks to calculate Λm from κ, or to compare Λm of strong vs weak electrolytes.
Kohlrausch's Law. JEE often gives λ° for ions and asks for Λm° of a salt, or to find λ° of an ion from data.
Degree of Dissociation (α) from Conductivity. JEE asks to find Ka of weak acid given Λm and Λm°.
Electrolytic Cells and Electrolysis. JEE often asks to predict products at electrodes for given electrolyte (e.g., NaCl, CuSO4).
Product Prediction in Electrolysis. JEE asks to predict products for electrolysis of aqueous solutions (e.g., CuSO4, AgNO3, NaCl).
Batteries and Fuel Cells. JEE may ask about reactions in dry cell, lead-acid battery, or H2-O2 fuel cell.
Corrosion. JEE may ask about rusting mechanism or methods of prevention (e.g., galvanization, sacrificial protection).
Relation Between ΔG°, E°, and K. JEE often asks to find K from E° or ΔG°, or to find E° from K.
Disproportionation Reactions. JEE asks to check spontaneity of disproportionation for given E° values.
Standard Hydrogen Electrode (SHE). JEE may ask about construction or use of SHE in measuring E°.
Cell Representation and Notation. JEE often asks to write cell notation from given half-reactions or to identify errors in notation.
Concentration Cells. JEE may ask to calculate Ecell for concentration cells or to determine direction of electron flow.

Common traps

Confusing oxidation with addition of oxygen only; remember it's about electron transfer. Oxidation and Reduction
Assigning O = -2 in peroxides (e.g., H2O2, O = -1) or superoxides. Oxidation Number Rules
Thinking the substance that is oxidized is the oxidizing agent; it's the opposite. Oxidizing and Reducing Agents
Forgetting to balance oxygen and hydrogen before electrons. Balancing Redox Reactions (Half-Reaction Method)
Confusing anode and cathode: anode is where oxidation occurs (negative in galvanic, positive in electrolytic). Electrochemical Cell
Using reduction potentials directly without subtracting; always subtract anode from cathode. Standard Electrode Potential (E°)
Using log base 10 vs ln; remember 0.0591 is for log10 at 298 K. Nernst Equation
Forgetting that n is number of moles of electrons transferred, not stoichiometric coefficient. Gibbs Free Energy and Cell Potential
Forgetting that K is dimensionless and uses activities, but concentrations are often used. Equilibrium Constant from E°
Thinking more negative E° means stronger oxidizing agent; it's the opposite. Electrochemical Series
Forgetting to convert time to seconds if given in minutes. Faraday's Laws of Electrolysis
Confusing conductivity (κ) with conductance (G); $κ = G \times G^{*}$ , where $G^{*} = l / A$ is the cell constant, so $G = κ / G^{*}$ . Conductance in Electrolytes
Forgetting to multiply by stoichiometric coefficients (ν). Kohlrausch's Law
Using this for strong electrolytes; α ≈ 1 for them. Degree of Dissociation (α) from Conductivity

Topics in Redox Reactions and Electrochemistry

Oxidation Number
Balancing Redox Reactions
Electrochemical Cells
Nernst Equation
Electrolysis
Conductance

Previous-year questions on Redox Reactions and Electrochemistry

JEEGenie has 501 previous-year questions on Redox Reactions and Electrochemistry. A few worked examples follow.

Year	Questions
2026	29
2025	33
2024	48
2023	39
2022	33
2021	35
2020	25
2019	39
2018	12
2017	11
2016	11
2015	9
2014	16
2013	12
2012	6
2011	6
2010	4
2009	4
2008	2
2007	10
2006	10
2005	6
2004	10
2003	7
2002	10
2001	4
2000	5
1999	2
1998	5
1997	4
1996	2
1995	1
1994	3
1993	3
1992	5
1991	4
1990	3
1989	4
1988	5
1987	3
1986	4
1985	4
1984	4
1983	3
1982	2
1981	2
1980	1
1978	1

Question 1 hard

Consider the following two half-cell reactions along with the standard reduction potential given :

{C O}_{2} + 6 H^{+} + 6 e^{-} ⟶ {C H}_{3} O H + H_{2} O E_{red}^{\circ} = 0.02 V \frac{1}{2} O_{2} + 2 H^{+} + 2 e^{-} ⟶ H_{2} O E_{red}^{\circ} = 1.23 V

A fuel cell was set up using the above two reactions such that the cell operates under the standard condition of 1 bar pressure and 298 K temperature. The fuel cell works with 80% efficiency. If the work derived from the cell using 1 mol of

{C H}_{3} O H

is used to compress an ideal gas isothermally against a constant pressure of 1 kPa, then the change in the volume of the gas,

Δ V = \underline{}

^{3}

. (nearest integer) Given :

F = 96500 {C m o l}^{- 1}

Answer: 560

Explanation. For the overall cell reaction, combine the two half-reactions so that electrons cancel:

C O_{2} + 6 H^{+} + 6 e^{-} \to C H_{3} O H + H_{2} O (E^{\circ} = 0.02 V)

3 (\frac{1}{2} O_{2} + 2 H^{+} + 2 e^{-} \to H_{2} O) (E^{\circ} = 1.23 V)

Overall:

C O_{2} + 2 H_{2} O \to C H_{3} O H + \frac{3}{2} O_{2}

But for the fuel cell, the spontaneous direction is the reverse:

C H_{3} O H + \frac{3}{2} O_{2} \to C O_{2} + 2 H_{2} O

with

n = 6

electrons transferred. Standard cell potential:

E_{cell}^{\circ} = E_{cathode}^{\circ} - E_{anode}^{\circ} = 1.23 - 0.02 = 1.21 V

Maximum work from 1 mol CH_{3}OH:

W_{\max} = n F E^{\circ} = 6 \times 96500 \times 1.21 = 700590 J

At 80% efficiency:

W_{actual} = 0.80 \times 700590 = 560472 J

This work is used to compress an ideal gas isothermally against constant external pressure

P = 1 k P a = 1000 P a

. Work done on the gas:

W = - P Δ V \Rightarrow Δ V = - \frac{W}{P}

Since the gas is compressed,

Δ V

is negative in magnitude, but the question asks for the change in volume (magnitude):

∣ Δ V ∣ = \frac{560472}{1000} = 560.472 m^{3}

Nearest integer:

560

From NTA/IIT papers: JEE Main 2026 · 2 Apr Shift 2

Question 2 medium

0.2 % (w / v)

solution of NaOH is measured to have resistivity

870.0 m Ω m

. The molar conductivity of the solution will be__________

\times 10^{2} m S {d m}^{2} {m o l}^{- 1}

. (Nearest integer)

Answer: 23

Explanation. **Step 1: Concentration.**

0.2 %

(w/v) means

0.2

g NaOH per

100

mL solution, i.e.

2

g/L. Molar mass of NaOH

= 40

g/mol, so

M = \frac{2}{40} = 0.05 mol/L = 0.05 {mol/dm}^{3} = 50 {mol/m}^{3}

. **Step 2: Conductivity.** Resistivity

ρ = 870.0 m Ω m = 0.8700 Ω m

κ = \frac{1}{ρ} = \frac{1}{0.870} \approx 1.1494 S/m

**Step 3: Molar conductivity (SI units).** Using

C

in mol/m

^{3}

gives

Λ_{m}

directly in S·m

^{2}

/mol:

Λ_{m} = \frac{κ}{C} = \frac{1.1494}{50} \approx 0.022989 S \cdot m^{2} / mol

Convert S to mS (

\times 1000

Λ_{m} \approx 22.989 mS \cdot m^{2} / mol

. **Step 4: Convert m

^{2}

to dm

^{2}

.** Since

1 m = 10 dm

1 m^{2} = 100 {dm}^{2}

, so:

Λ_{m} \approx 22.989 \times 100 = 2298.9 mS \cdot {dm}^{2} / mol

**Step 5: Express as

\times 10^{2}

.**

2298.9 = 22.989 \times 10^{2} \approx 23 \times 10^{2}

Answer: 23

From NTA/IIT papers: JEE Main 2025 · 2 Apr Shift 2

Question 3 easy

One of the commonly used electrode is calomel electrode. Under which of the following categories, calomel electrode comes?

Metal ion - Metal electrodes
Oxidation - Reduction electrodes
Metal - Insoluble Salt - Anion electrodes
Gas - Ion electrodes

Answer: C

Explanation. A calomel electrode consists of mercury in contact with mercury(I) chloride,

H g_{2} C l_{2}

(calomel), which is a sparingly soluble salt, along with potassium chloride solution. Its construction is:

H g (l) ∣ H g_{2} C l_{2} (s) ∣ K C l (a q)

The electrode reaction is:

H g_{2} C l_{2} (s) + 2 e^{-} ⇌ 2 H g (l) + 2 C l^{-}

Here, a metal (Hg) is in contact with its insoluble salt (

H g_{2} C l_{2}

), and the potential depends on the concentration of the anion (

C l^{-}

) in solution. This is the defining feature of a **metal–insoluble salt–anion electrode**, where the metal is coated with its sparingly soluble salt and dipped in a solution containing the corresponding anion. It is not a simple metal-ion/metal electrode (no

H g^{2 +}

in solution), not a redox electrode (no two soluble species in different oxidation states), and not a gas-ion electrode (no gas involved). Answer: (C)

From NTA/IIT papers: JEE Main 2024 · 4 Apr Shift 1

Question 4 hard

The reduction potential (

E^{0}

, in V) of

M n O_{4}^{-} (a q) / M n (s)

is ______. [Given:

E_{(M n O_{4}^{-} (a q) / M n O_{2} (s))}^{0} = 1.68 V

;

E_{(M n O_{2} (s) / M n^{2 +} (a q))}^{0} = 1.21 V

;

E_{(M n^{2 +} (a q) / M n (s))}^{0} = - 1.03 V

]

Answer: 0.77

Explanation. For the overall reduction,

M n O_{4}^{-} + 8 H^{+} + 5 e^{-} \to M n^{2 +} + 4 H_{2} O

we need the standard potential. We are given three half-reactions: 1.

M n O_{4}^{-} + 4 H^{+} + 3 e^{-} \to M n O_{2} + 2 H_{2} O, E_{1}^{0} = 1.68 V

M n O_{2} + 4 H^{+} + 2 e^{-} \to M n^{2 +} + 2 H_{2} O, E_{2}^{0} = 1.21 V

M n^{2 +} + 2 e^{-} \to M n, E_{3}^{0} = - 1.03 V

We want

M n O_{4}^{-} + 8 H^{+} + 5 e^{-} \to M n^{2 +} + 4 H_{2} O

which is reaction (1) + reaction (2). The Gibbs free energy change for the sum is

Δ G^{0} = - n_{1} F E_{1}^{0} - n_{2} F E_{2}^{0}

with

n_{1} = 3, n_{2} = 2

, so total

n = 5

. Thus

- 5 F E^{0} = - 3 F (1.68) - 2 F (1.21)

5 E^{0} = 3 (1.68) + 2 (1.21) = 5.04 + 2.42 = 7.46

E_{M n O_{4}^{-} / M n^{2 +}}^{0} = \frac{7.46}{5} = 1.492 V

Now combine with reaction (3) to get

M n O_{4}^{-} \to M n

M n O_{4}^{-} + 8 H^{+} + 5 e^{-} \to M n^{2 +} + 4 H_{2} O, E^{0} = 1.492 V

M n^{2 +} + 2 e^{-} \to M n, E^{0} = - 1.03 V

Total electrons:

5 + 2 = 7

Δ G_{total}^{0} = - 5 F (1.492) - 2 F (- 1.03) = - 7.46 F + 2.06 F = - 5.40 F

For 7 electrons,

- 7 F E_{overall}^{0} = - 5.40 F ⟹ E_{overall}^{0} = \frac{5.40}{7} = 0.7714 V

0.77

From NTA/IIT papers: JEE Advanced 2022

Frequently asked questions

How much of JEE Main comes from Redox Reactions and Electrochemistry?: JEEGenie estimates about 5% of JEE Main marks come from Redox Reactions and Electrochemistry, based on recent papers. The share varies from year to year.
Which formulas matter most in Redox Reactions and Electrochemistry?: The Redox Reactions and Electrochemistry sheet on this page has 12 formula entries, starting with Standard Electrode Potential (E°), Nernst Equation, Gibbs Free Energy and Cell Potential, Equilibrium Constant from E°, Faraday's Laws of Electrolysis. Each one comes with when to use it and the trap to avoid.
What topics does Redox Reactions and Electrochemistry cover for JEE?: Redox Reactions and Electrochemistry covers Oxidation Number, Balancing Redox Reactions, Electrochemical Cells, Nernst Equation, Electrolysis, Conductance.
How should I revise Redox Reactions and Electrochemistry before the exam?: Learn each formula together with its condition of use, read the trap listed beside it, then practise questions and review every mistake. The practice link on this page opens Redox Reactions and Electrochemistry questions on JEEGenie.
How many previous-year questions are there on Redox Reactions and Electrochemistry?: JEEGenie has 501 previous-year questions on Redox Reactions and Electrochemistry, and this page shows a few with worked explanations.
Is practice on Redox Reactions and Electrochemistry free on JEEGenie?: Sign-up is free and includes a 7-day Pro trial. After the trial, free accounts keep a limited daily quota.