Key Fact
Common batteries
Dry cell (Leclanché): Zn anode, MnO₂/C cathode, ~1.5 V. Lead accumulator: Pb anode, PbO₂ cathode, H₂SO₄ electrolyte, ~2 V/cell. Fuel cell: H₂/O₂ → H₂O + electrical energy.
-- NCERT Class 12 Chemistry, Ch. 2, p. 54Fuel Cells
8 MCQs9-step worked example
Source: NCERT Redox Reactions and ElectrochemistryOfficial key: NTA-verifiedLast updated: 26 Sep 2026
Fuel Cells, explained for NEET
A fuel cell converts chemical energy of a fuel directly into electrical energy without combustion. The key difference from a conventional galvanic cell: reactants are continuously supplied from an external source rather than stored inside the cell.
The hydrogen–oxygen fuel cell is the NCERT-standard example (NCERT Class 12 Chemistry Chapter 2, page 56). At the anode, hydrogen is oxidised; at the cathode, oxygen is reduced. The overall reaction is:
2H₂(g) + O₂(g) → 2H₂O(l)
The electrodes are porous carbon or platinum, and the electrolyte is typically concentrated KOH or a proton-exchange membrane.
Half-reactions (alkaline medium):
- Anode: 2H₂ + 4OH⁻ → 4H₂O + 4e⁻
- Cathode: O₂ + 2H₂O + 4e⁻ → 4OH⁻
Why NEET cares about fuel cells:
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Efficiency advantage. Fuel cells bypass the Carnot-cycle limitation of heat engines. They convert chemical energy to electrical energy in a single step, achieving efficiencies of 60–70% — higher than thermal power plants (~40%).
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Clean product. The only product of a hydrogen–oxygen fuel cell is water. No CO₂, no SO₂, no particulates.
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Continuous operation. Unlike a dry cell or lead-acid battery that runs down, a fuel cell operates as long as fuel and oxidant are supplied. It is not "recharged" — fresh reactants are fed in.
Common confusion: Students conflate fuel cells with rechargeable batteries. A fuel cell is NOT rechargeable — it does not store energy internally. A lead-acid battery stores reactants inside and can be recharged by reversing the reaction; a fuel cell requires an external fuel supply.
Watch-out: Questions may test whether a fuel cell is a primary cell, secondary cell, or neither. It is classified as a primary cell (non-rechargeable) in NCERT treatment, but distinguished from ordinary primary cells by continuous fuel supply.
Can you answer these Fuel Cells 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
In a hydrogen–oxygen fuel cell, the overall cell reaction produces:
Show answer and why every option is right or wrong
Answer: D. The overall reaction is 2H₂(g) + O₂(g) → 2H₂O(l). Water is the sole product (NCERT Class 12 Chemistry Chapter 2, page 56).
Why A is wrong: A is wrong because hydrogen peroxide (H₂O₂) is not produced in a fuel cell. The complete reduction of O₂ in a fuel cell yields water, not a peroxide intermediate.
Why B is wrong: B is wrong because H₂ and O₂ are the reactants consumed in the cell, not the products.
Why C is wrong: C is wrong because ozone (O₃) is an allotrope of oxygen formed under UV or electrical discharge conditions, not in a fuel cell reaction.
MCQ 2Easy RecallPractice
A fuel cell differs from an ordinary galvanic cell primarily because:
Show answer and why every option is right or wrong
Answer: B. The defining feature of a fuel cell is continuous external supply of fuel and oxidant, unlike a galvanic cell where reactants are sealed inside (NCERT Class 12 Chemistry Chapter 2, page 56).
Why A is wrong: A is wrong because salt bridges (or membranes serving a similar function) can be present in both galvanic cells and fuel cells. This is not the distinguishing feature.
Why C is wrong: C is wrong because fuel cells do have electrodes — typically porous carbon or platinum electrodes where the half-reactions occur.
Why D is wrong: D is wrong because fuel cells produce direct current (DC), same as all electrochemical cells.
MCQ 3Easy RecallPractice
In a hydrogen–oxygen fuel cell using alkaline (KOH) electrolyte, the cathode reaction is:
Show answer and why every option is right or wrong
Answer: A. In alkaline medium, the cathode (reduction) half-reaction is O₂ + 2H₂O + 4e⁻ → 4OH⁻ (NCERT Class 12 Chemistry Chapter 2, page 56).
Why B is wrong: B is wrong because this is the anode (oxidation) half-reaction in alkaline medium, not the cathode reaction.
Why C is wrong: C is wrong because this cathode reaction uses H⁺ ions, which corresponds to an acidic/PEM fuel cell, not an alkaline KOH electrolyte cell.
Why D is wrong: D is wrong because this is an oxidation half-reaction (loss of electrons by H₂) and uses H⁺ — it represents neither the cathode reaction nor the alkaline medium.
MCQ 4Direct ApplicationPractice
A fuel cell achieves higher efficiency than a thermal power plant because:
Show answer and why every option is right or wrong
Answer: B. Fuel cells convert chemical energy directly to electrical energy without an intermediate combustion/heat step, so they are not limited by the Carnot efficiency ceiling that constrains heat engines (NCERT Class 12 Chemistry Chapter 2, page 56).
Why A is wrong: A is wrong because while platinum serves as an effective electrode catalyst, the higher efficiency is due to the direct energy conversion pathway, not the conductivity of the electrode material.
Why C is wrong: C is wrong because fuel cells actually operate at relatively moderate temperatures (compared to combustion engines). High temperature is not the source of their efficiency advantage.
Why D is wrong: D is wrong because efficiency refers to the fraction of fuel energy converted to useful work, not to energy density. A fuel cell converts a larger fraction of the available energy, regardless of the absolute energy content per unit mass.
MCQ 5Direct ApplicationPractice
Which statement correctly classifies a hydrogen–oxygen fuel cell?
Show answer and why every option is right or wrong
Answer: A. A fuel cell is classified as a primary cell — the cell reaction cannot be reversed by passing current. Refilling fuel is not the same as electrochemical recharging (NCERT Class 12 Chemistry Chapter 2, page 54).
Why B is wrong: B is wrong because 'recharging' in electrochemistry means reversing the cell reaction by applying external current. A fuel cell's reaction (H₂ + O₂ → H₂O) is not reversed inside the cell; fresh reactants are supplied externally.
Why C is wrong: C is wrong because fuel cells do use solid electrodes (porous carbon or platinum). The classification as primary or secondary depends on reaction reversibility, not electrode state.
Why D is wrong: D is wrong because refilling reactants is a mechanical resupply, not electrochemical recharging. Secondary cells like lead-acid batteries regenerate their original reactants in situ when current is reversed.
MCQ 6Direct ApplicationPractice
The electrode material commonly used in a hydrogen–oxygen fuel cell is:
Show answer and why every option is right or wrong
Answer: C. Porous carbon impregnated with catalyst (or platinum electrodes) is used to provide a large surface area for the gas-phase reactions at both electrodes (NCERT Class 12 Chemistry Chapter 2, page 56).
Why A is wrong: A is wrong because zinc is used as the anode in dry cells (Leclanché cell) and Daniel cells, not in fuel cells.
Why B is wrong: B is wrong because lead dioxide (PbO₂) is the cathode material in lead-acid batteries, not in hydrogen–oxygen fuel cells.
Why D is wrong: D is wrong because mercury is used in mercury cells (button cells), not in fuel cells. Mercury has no catalytic role in H₂/O₂ reactions.
MCQ 7Concept TrapPractice
A student claims: "A fuel cell is like a rechargeable battery because you can keep using it indefinitely." Which correction is accurate?
Show answer and why every option is right or wrong
Answer: C. A rechargeable (secondary) battery regenerates its reactants in situ by reversing current. A fuel cell operates continuously because fresh fuel is supplied externally — a fundamentally different mechanism (NCERT Class 12 Chemistry Chapter 2, page 56).
Why A is wrong: A is wrong because fuel cells are classified as primary cells. 'Recharging' specifically means reversing the electrochemical reaction, which a fuel cell does not do.
Why B is wrong: B is wrong because fuel cells can operate indefinitely as long as fuel and oxidant are supplied. There is no inherent fixed lifetime for the reaction itself.
Why D is wrong: D is wrong because there is no intrinsic time limit. Fuel cells in spacecraft have operated continuously for extended missions.
MCQ 8Concept TrapPractice
Why is water the only product in a hydrogen–oxygen fuel cell, while burning hydrogen in air also produces water but with significant energy lost as heat?
Show answer and why every option is right or wrong
Answer: D. Both processes have the same overall reaction (2H₂ + O₂ → 2H₂O), but the fuel cell channels the electron transfer through an external circuit as electrical work, bypassing the combustion/heat intermediate that thermal engines use (NCERT Class 12 Chemistry Chapter 2, page 56).
Why A is wrong: A is wrong because the fuel cell produces H₂O directly, not H₂O₂. The overall reaction is identical to combustion: 2H₂ + O₂ → 2H₂O.
Why B is wrong: B is wrong because fuel cells operate at moderate temperatures (typically 60–200°C depending on type), not at absolute zero. Some thermal loss still occurs, but it is much less than in combustion engines.
Why C is wrong: C is wrong because the catalyst (platinum) lowers activation energy but does not change the products. Both combustion and fuel cell reaction produce water.
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How do you solve a Fuel Cells question? A worked example
- 1
Given
A hydrogen–oxygen fuel cell with alkaline (KOH) electrolyte operates at standard conditions. The student is asked to write the half-reactions and the overall reaction, then explain why this cell cannot be classified as a secondary cell.
- 2
Required
(a) Anode and cathode half-reactions in alkaline medium.
(b) Overall cell reaction.
(c) Classification with justification. - 3
Concept
In a fuel cell, hydrogen is oxidised at the anode and oxygen is reduced at the cathode. The electrolyte medium determines the form of the half-reactions (OH⁻ ions appear in alkaline medium). Classification depends on whether the reaction is reversible by applying external current.
- 4
Formula
No numerical formula is needed. The half-reactions are:• Anode: 2H₂(g) + 4OH⁻(aq) → 4H₂O(l) + 4e⁻• Cathode: O₂(g) + 2H₂O(l) + 4e⁻ → 4OH⁻(aq)
- 5
Substitution
Adding the two half-reactions:
2H₂(g) + 4OH⁻ + O₂(g) + 2H₂O → 4H₂O + 4e⁻ + 4OH⁻ + (−4e⁻) - 6
Calculation
Cancel species appearing on both sides: 4OH⁻ cancels, 4e⁻ cancels, and 2H₂O cancels from the 4H₂O product.
Overall: 2H₂(g) + O₂(g) → 2H₂O(l) - 7
Final answer
(a) Anode: 2H₂ + 4OH⁻ → 4H₂O + 4e⁻; Cathode: O₂ + 2H₂O + 4e⁻ → 4OH⁻
(b) Overall: 2H₂(g) + O₂(g) → 2H₂O(l)
(c) Primary cell — the reaction is not reversed by applying external current. Continuous operation comes from external fuel supply, not electrochemical recharging. - 8
Common trap
Confusing "refilling fuel" with "recharging." Recharging means reversing the cell reaction electrochemically (as in a lead-acid battery). A fuel cell never reverses its reaction — it is mechanically resupplied.
- 9
Similar NEET-style question
"A hydrogen–oxygen fuel cell uses an acid electrolyte (H₃PO₄). Write the half-reactions at each electrode and explain how they differ from the alkaline-medium half-reactions."
(Answer: Anode: H₂ → 2H⁺ + 2e⁻; Cathode: O₂ + 4H⁺ + 4e⁻ → 2H₂O. The ion carrier changes — H⁺ migrates through the electrolyte in acid medium, OH⁻ in alkaline — but the overall reaction remains 2H₂ + O₂ → 2H₂O.)
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What to remember before solving Fuel Cells questions
More in Redox Reactions and Electrochemistry: 4 exam traps and mistakes · 5 formulas · 2 question patterns from its other lessons.
Fuel Cells questions from past NEET papers
No question in our NEET 2020–2025 set targets this topic directly.
All 21 past-paper questions from Redox Reactions and Electrochemistry →
Sources
NCERT refs: Class 12 Chemistry Chapter 2, p.56
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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