Definition
Standard electrode potential
E° measured under standard conditions (1 M, 1 bar, 298 K) relative to standard hydrogen electrode (SHE, E° = 0). Higher E°: stronger oxidising agent.
-- NCERT Class 11 Chemistry, Ch. 7, p. 250Electrode Potential
8 MCQs2 revision cards9-step worked example
Source: NCERT Redox Reactions and ElectrochemistryPYQ coverage: NEET 2022, 2026Official key: NTA-verifiedLast updated: 25 Sep 2026
Electrode Potential, explained for NEET
Electrode Potential and Standard Electrode Potential
Every metal dipped into a solution of its own ions develops a potential difference at the metal-solution interface. This is the electrode potential — it measures a half-cell's tendency to gain electrons (get reduced). You cannot measure a single electrode's absolute potential; you always measure it relative to a reference.
The reference: the Standard Hydrogen Electrode (SHE) is assigned E° = 0.000 V at 298 K, 1 bar H₂, 1 M H⁺ (NCERT Class 12 Chemistry Chapter 2, page 34). Every other electrode potential in the electrochemical series is measured against SHE.
Convention trap that costs marks: NCERT and NEET use the reduction potential convention — all tabulated values are for the reduction half-reaction. When you calculate cell EMF:
E°_cell = E°(cathode) − E°(anode)
Both values are reduction potentials. Do NOT flip the sign of the anode value before subtracting — the subtraction already accounts for the reversal.
Moving beyond standard conditions: when concentrations differ from 1 M or temperature from 298 K, the Nernst equation adjusts the potential:
E = E° − (0.0591/n) × log₁₀ Q (at 298 K)
Here n is the number of electrons transferred in the balanced redox equation, and Q is the reaction quotient. A high-frequency trap: getting n wrong. For Zn²⁺/Zn vs Cu²⁺/Cu, the balanced equation transfers 2 electrons (n = 2). For Cr₂O₇²⁻ reduction in acid, n = 6. Always write the balanced equation first, then count electrons.
Watch-out: when Q = 1, log Q = 0 and E = E°. At equilibrium, E = 0 and Q = K. These limiting checks catch arithmetic errors fast.
Can you answer these Electrode Potential MCQs?
Select an option to see the explanation. Wrong answers show why your choice was tempting — and name the exact trap it exploits.
MCQ 1Easy RecallPractice
The standard electrode potential of a half-cell is measured relative to which reference electrode?
Show answer and why every option is right or wrong
Answer: C. By IUPAC convention, the standard hydrogen electrode (SHE) is assigned E° = 0.000 V and serves as the universal reference for all standard electrode potentials (NCERT Class 12 Chemistry Chapter 2, page 34).
Why A is wrong: A is wrong because the calomel electrode is a secondary reference electrode used in laboratory practice; it is not the IUPAC-defined primary reference. Its own potential (+0.242 V) is measured against SHE.
Why B is wrong: B is wrong because the Ag/AgCl electrode is another secondary reference. Like calomel, its potential is defined relative to SHE, not the other way around.
Why D is wrong: D is wrong because no 'saturated copper electrode' is an established reference standard. This is a fabricated distractor.
MCQ 2Easy RecallPractice
In the IUPAC convention, the standard electrode potentials listed in the electrochemical series represent which type of potential?
Show answer and why every option is right or wrong
Answer: D. IUPAC convention tabulates all standard electrode potentials as reduction potentials — the potential for the half-reaction written as a reduction (NCERT Class 12 Chemistry Chapter 2, page 34).
Why A is wrong: A is wrong because the oxidation potential convention (used in older American textbooks) is the negative of the reduction potential. IUPAC and NCERT use reduction potentials exclusively.
Why B is wrong: B is wrong because decomposition potential refers to the minimum voltage needed to electrolyse a compound — an electrolysis concept, not a thermodynamic electrode property.
Why C is wrong: C is wrong because cell potential is the difference between two half-cell potentials, not a property of a single electrode.
MCQ 3Easy RecallPractice
At equilibrium, the cell potential E of an electrochemical cell equals:
Show answer and why every option is right or wrong
Answer: A. At equilibrium the driving force for the net reaction is zero, so E = 0. From the Nernst equation, when E = 0 the reaction quotient Q equals the equilibrium constant K (NCERT Class 12 Chemistry Chapter 2, page 34).
Why B is wrong: B is wrong because E° is the standard cell potential (at Q = 1). At equilibrium Q = K ≠ 1 (for a spontaneous cell), so E ≠ E°.
Why C is wrong: C is wrong because +1 V is an arbitrary value with no thermodynamic basis at equilibrium.
Why D is wrong: D is wrong because −nF has units of C/mol (charge), not volts. This confuses the ΔG = −nFE relationship with the cell potential itself.
MCQ 4Direct ApplicationPractice
Given: E°(Cu²⁺/Cu) = +0.34 V, E°(Zn²⁺/Zn) = −0.76 V. What is E°_cell for the Daniell cell (Zn anode, Cu cathode)?
Show answer and why every option is right or wrong
Answer: B. E°_cell = E°(cathode) − E°(anode) = (+0.34) − (−0.76) = +1.10 V. Both values enter as reduction potentials; the formula handles the sign reversal (NCERT Class 12 Chemistry Chapter 2, page 34).
Why A is wrong: A is wrong because +0.42 V results from adding the two potentials with wrong signs — typically from flipping the cathode sign instead of subtracting the anode reduction potential directly.
Why C is wrong: C is wrong because −1.10 V reverses cathode and anode in the formula (subtracts cathode from anode). A negative E°_cell would mean the reaction is non-spontaneous, contradicting the known spontaneity of the Daniell cell.
Why D is wrong: D is wrong because −0.42 V combines both errors: wrong subtraction order and wrong sign handling.
MCQ 5Direct ApplicationPractice
For the cell Zn | Zn²⁺ (1 M) || Cu²⁺ (0.01 M) | Cu, how many electrons (n) should be used in the Nernst equation?
Show answer and why every option is right or wrong
Answer: A. The balanced cell reaction is Zn + Cu²⁺ → Zn²⁺ + Cu. Each Zn atom loses 2 electrons and each Cu²⁺ gains 2 electrons, so n = 2. This is determined from the balanced redox equation, not from the stoichiometric coefficients of the ions alone.
Why B is wrong: B is wrong because n = 1 would apply only to a one-electron transfer process (e.g., Ag⁺/Ag). For Cu²⁺ + 2e⁻ → Cu, two electrons transfer per formula unit. Using n = 1 doubles the Nernst correction term and gives an incorrect EMF (trap: nernst n electrons negmark).
Why C is wrong: C is wrong because n = 3 corresponds to a three-electron process (e.g., Al³⁺/Al). Neither Zn²⁺/Zn nor Cu²⁺/Cu involves a 3-electron transfer.
Why D is wrong: D is wrong because n = 4 would require a four-electron balanced equation. No single Zn or Cu half-reaction transfers 4 electrons.
MCQ 6Direct ApplicationPractice
For a cell with E° = +0.46 V and n = 2, what is the cell EMF when the reaction quotient Q = 10 at 298 K? (Use: E = E° − (0.0591/n) log Q)
Show answer and why every option is right or wrong
Answer: D. E = 0.46 − (0.0591/2) × log₁₀(10) = 0.46 − 0.02955 × 1 = 0.430 V (3 s.f.). The Nernst correction is (0.0591/2) × 1 = 0.02955 V.
Why A is wrong: A is wrong because +0.46 V is the standard EMF (at Q = 1). When Q = 10, the Nernst correction is non-zero, so E < E°.
Why B is wrong: B is wrong because +0.519 V makes two slips: it adds the correction instead of subtracting it, and uses n = 1: 0.46 + 0.0591 = 0.519. When Q > 1 the correction lowers E.
Why C is wrong: C is wrong because +0.401 V results from using n = 1 instead of n = 2 in the Nernst equation: 0.46 − 0.0591 × 1 = 0.401. This is the classic n-electron error (trap: nernst n electrons negmark).
MCQ 7CalculationPractice
For the cell: Ag | Ag⁺ (0.001 M) || Ag⁺ (1 M) | Ag (a concentration cell), calculate E_cell at 298 K. E° for Ag⁺/Ag = +0.80 V.
Show answer and why every option is right or wrong
Answer: C. For a concentration cell, E°_cell = 0 (same electrodes). The Nernst equation gives E = 0 − (0.0591/1) × log₁₀(0.001/1) = −0.0591 × (−3) = +0.177 V. Here n = 1 (Ag⁺ + e⁻ → Ag), and Q = [Ag⁺]_anode / [Ag⁺]_cathode = 0.001/1 = 10⁻³.
Why A is wrong: A is wrong because E = 0 V would be the case only if both compartments had the same concentration. The concentration difference is the driving force of this cell.
Why B is wrong: B is wrong because +0.0591 V results from using log₁₀(0.001) = −3 but then dividing by n = 3 instead of n = 1, or equivalently using log₁₀(0.1) = −1 with n = 1. The Ag⁺/Ag half-reaction is a one-electron process.
Why D is wrong: D is wrong because +0.80 V is the standard reduction potential of Ag⁺/Ag. In a concentration cell, E°_cell = 0 (both electrodes are identical), so the standard potential of the individual half-cell does not appear as the cell EMF.
MCQ 8Concept TrapPractice
A student calculates E_cell for a Daniell cell using the Nernst equation and obtains a negative value. Which of the following is the most likely interpretation?
Show answer and why every option is right or wrong
Answer: B. A negative E_cell means the forward reaction is non-spontaneous under those specific conditions — the reaction proceeds spontaneously in the reverse direction. This can happen at extreme concentration ratios (very large Q), even for a Daniell cell whose E° is positive.
Why A is wrong: A is wrong because at equilibrium E = 0 exactly, not a negative value. A negative E_cell indicates the system is past equilibrium for the forward reaction.
Why C is wrong: C is wrong because while E° for the Daniell cell is positive (+1.10 V), the actual EMF under non-standard conditions depends on Q. If Q is extremely large (products heavily favoured), E can become negative via the Nernst equation.
Why D is wrong: D is wrong because temperature alone does not determine the sign of E_cell. The Nernst equation at temperatures other than 298 K uses RT/nF instead of 0.0591/n, but Q is the dominant factor driving E negative.
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Electrode Potential: quick recall before you leave
How do you solve a Electrode Potential question? A worked example
Pattern: Nernst equation problem (NEET pattern: nernst equation problem)
- 1
Given
• E°(Cu²⁺/Cu) = +0.34 V• E°(Zn²⁺/Zn) = −0.76 V• [Zn²⁺] = 0.10 M• [Cu²⁺] = 2.0 M• T = 298 K
- 2
Required
E_cell at the given non-standard concentrations.
- 3
Concept
The Nernst equation adjusts the standard EMF for non-standard concentrations via the reaction quotient Q.
- 4
Formula
E°_cell = E°(cathode) − E°(anode)
E = E° − (0.0591/n) × log₁₀ Q - 5
Substitution
E°_cell = (+0.34) − (−0.76) = +1.10 V
Balanced reaction: Zn(s) + Cu²⁺(aq) → Zn²⁺(aq) + Cu(s)
n = 2 (Zn loses 2e⁻, Cu²⁺ gains 2e⁻)
Q = [Zn²⁺]/[Cu²⁺] = 0.10/2.0 = 0.050
E = 1.10 − (0.0591/2) × log₁₀(0.050) - 6
Calculation
log₁₀(0.050) = log₁₀(5.0 × 10⁻²) = log₁₀(5.0) + log₁₀(10⁻²) = 0.699 − 2 = −1.301
(0.0591/2) × (−1.301) = 0.02955 × (−1.301) = −0.03845
E = 1.10 − (−0.03845) = 1.10 + 0.03845 = 1.138 V
Note on exact values: the integer 2 in n = 2 is a counting number (electrons per balanced equation) and does not limit significant figures. The factor 0.0591 is a derived constant (RT ln10 / F at 298 K) carrying 3 significant figures, which governs the precision of the correction term. - 7
Final answer
E_cell = 1.14 V (3 significant figures, limited by the 0.0591 factor).
- 8
Common trap
Using n = 1 instead of n = 2 would double the correction: (0.0591/1) × (−1.301) = −0.0769, giving E = 1.177 V — a wrong answer that appears on NEET option lists. Always count electrons from the balanced equation.
- 9
Similar NEET-style question
For the cell Fe | Fe²⁺ (0.01 M) || Ag⁺ (0.1 M) | Ag, calculate E_cell at 298 K. Given: E°(Fe²⁺/Fe) = −0.44 V, E°(Ag⁺/Ag) = +0.80 V. (Hint: balanced reaction transfers n = 2 electrons; Q = [Fe²⁺]/[Ag⁺]².)
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What to remember before solving Electrode Potential questions
Definition
Standard electrode potential
E° = potential of electrode at unit activity (1 M for ions, 1 bar for gases, 298 K) relative to SHE (E° = 0 by definition). Higher E°: stronger tendency to be reduced.
-- NCERT Class 12 Chemistry, Ch. 2, p. 36More in Redox Reactions and Electrochemistry: 4 exam traps and mistakes · 5 formulas · 2 question patterns from its other lessons.
Electrode Potential questions from past NEET papers
2 questions from NEET 2022, 2026. Answers verified against NTA official keys.
NEET 2026
1+0.40 V
2+0.76 V
3−0.48 V
4+0.92 V
NTA Answer: Option 2(final)
NEET 2022
12CuSO4(aq) + 2Ag(s) → 2Cu(s) + Ag2SO4(aq)
2CuSO4(aq) + Zn(s) → ZnSO4(aq) + Cu(s)
3CuSO4(aq) + Fe(s) → FeSO4(aq) + Cu(s)
4FeSO4(aq) + Zn(s) → ZnSO4(aq) + Fe(s)
NTA Answer: Option 1(final)
All 21 past-paper questions from Redox Reactions and Electrochemistry →
Sources
NCERT refs: Class 12 Chemistry Chapter 2, p.34
Page numbers are the ones printed in the current NCERT textbook (2023 rationalised edition), unless marked pre-2023. The books are free at ncert.nic.in.
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