Fuels and Energy Sources – NDA Chemistry PYQs

NDA 2025-II

Q. 1.  Which one of the following is known as ‘water gas’?

(a) H₂O + CO₂

(b) NH₃

(c) H₂ + N₂

(d) CO + H₂

Answer: (d) CO + H₂

Explanation: Water gas = CO + H₂. NH₃ is ammonia. H₂ + N₂ is the feedstock for ammonia (Haber process). CO₂ + H₂O is not water gas. Concept Tested: Water gas = CO + H₂ (repeated)

★ JOVIK Exam Insight: Water gas (CO + H₂) has been asked in NDA 2014-I, 2015-II, 2016-I, 2018-II, 2024-I and 2025-II. It is one of the most repeated single facts in chemistry PYQs.

NDA 2024-I

Q. 2.  Water gas is a mixture of:

(a)  CO₂ and H₂

(b)  CO and H₂

(c)  CO₂ and H₂O

(d)  CO and H₂O

Answer: (b) CO and H₂

Explanation: Water gas = CO + H₂. This is produced by passing steam over hot coke: C + H₂O → CO + H₂. Concept Tested: Water gas = CO + H₂ (repeated)

NDA 2022-I

Q. 3.  Refining of petroleum is carried out using which one of the following techniques?

(a) Evaporation

(b) Fractional distillation

(c) Separating funnel

(d) Sublimation

Answer: (b) Fractional distillation

Explanation: Petroleum is refined by fractional distillation in a fractionating column. The crude oil is heated and different fractions (petrol, kerosene, diesel, fuel oil) are separated at different temperatures based on their boiling points. Concept Tested: Petroleum refining – fractional distillation

NDA 2021-I

Q. 4.  Which one of the following is the largest composition in biogas?

(a) Carbon dioxide

(b) Methane

(c) Hydrogen

(d) Hydrogen sulphide

Answer: (b) Methane

Explanation: Same question as NDA 2020 Q140. Methane is the largest constituent of biogas. Concept Tested: Largest component of biogas = methane (repeated)

NDA 2020

Q. 5.  Which one of the following is the major constituent of biogas?

(a) Carbon dioxide

(b) Nitrous oxide

(c) Methane

(d) Oxygen

Answer: (c) Methane

Explanation: Same question as NDA 2019-II Q91. Biogas is mainly methane. Concept Tested: Major constituent of biogas = methane (repeated)

Q. 6.  Which one of the following is the largest composition in biogas?

(a) Carbon dioxide

(b) Methane

(c) Hydrogen

(d) Hydrogen sulphide

Answer: (b) Methane

Explanation: Methane constitutes the largest proportion of biogas (55–70%). CO₂ is second. H₂ and H₂S are trace components. Concept Tested: Largest component of biogas = methane

NDA 2019-II

Q. 7.  Which one of the following is the major constituent of biogas?

(a) Carbon dioxide

(b) Nitrous oxide

(c) Methane

(d) Oxygen

Answer: (c) Methane

Explanation: Biogas is mainly methane (CH₄, ~55–70%). CO₂ makes up the rest. Concept Tested: Biogas = mainly methane (repeated)

NDA 2019-I

Q. 8.  Which one of the following is an example of a clean fuel?

(a) Coke

(b) Propane

(c) Petrol

(d) Wax

Answer: (b) Propane

Explanation: Clean fuels are those that produce little or no harmful byproducts (soot, particulates, heavy emissions) on combustion. Propane (LPG) is considered a relatively clean fuel compared to coal (coke), petrol or wax, which produce more soot and pollutants. Concept Tested: Clean fuel – propane (LPG) produces fewer pollutants

NDA 2018-II

Q. 9.  Which one of the following is called ‘syngas’?

(a) C(s) + H₂O(g)

(b) CO(g) + H₂O(g)

(c) CO(g) + H₂(g)

(d) NO₂(g) + H₂(g)

Answer: (c) CO(g) + H₂(g)

Explanation: Syngas (synthesis gas) is a mixture of CO and H₂. It is used to synthesise methanol, ammonia and other chemicals. Option (a) and (b) show reactants/products, not gas mixtures. Option (d) is not syngas. Concept Tested: Syngas = CO + H₂

NDA 2016-II

Q. 10.  The LPG cooking gas contains propane and butane as the constituents. A sulfur containing compound is added to the LPG, because

(a) it lowers the cost of production

(b) it enhances the efficiency of LPG

(c) it facilitates easy detection of leakage of the gas

(d) it assists in liquefying hydrocarbons

Answer: (c) it facilitates easy detection of leakage of the gas

Explanation: LPG (propane + butane) is odourless and colourless. A sulphur compound (ethanethiol or mercaptan) is added as an odorant so that gas leaks can be detected by smell. This is a safety measure. Concept Tested: LPG odorant – sulphur compound for leak detection

NDA 2016-I

Q. 11.  Statement I : Petroleum is a mixture of many different hydrocarbons of different densities. Statement II : The grade of petroleum depends mainly on the relative proportion of the different hydrocarbons.

(a) Both the Statements are individually true and Statement II is the correct explanation of Statement I.

(b) Both the Statements are individually true but Statement II is not the correct explanation of Statement I.

(c) Statement I is true but Statement II is false.

(d) Statement I is false but Statement II is true.

Answer: (b) Both the Statements are individually true but Statement II is not the correct explanation of Statement I.

Explanation: Petroleum is indeed a complex mixture of hydrocarbons (Statement I correct). The quality/grade of petroleum (as in crude oil grades) is primarily determined by the specific gravity, sulphur content and proportion of heavier vs lighter fractions (Statement II is broadly true). However, Statement II’s explanation does not fully or directly explain why different hydrocarbons have different densities (Statement I). Concept Tested: Petroleum as hydrocarbon mixture – composition determines grade

Q. 12.  Which one of the following is water gas ?

(a) Mixture of carbon monoxide and hydrogen

(b) Mixture of carbon monoxide and nitrogen

(c) Mixture of carbon dioxide and water vapour

(d) Mixture of carbon monoxide and water vapour

Answer: (a) Mixture of carbon monoxide and hydrogen

Explanation: Water gas = CO + H₂. Producer gas = CO + N₂. Syngas also = CO + H₂. Option (b) is producer gas. Option (c) is not a named gas mixture. Option (d) is not water gas. Concept Tested: Water gas = CO + H₂

NDA 2015-II

Q. 13.  Consider the following reaction: CH₄(g) + H₂O(g) ―1270 K→ CO(g) + 3H₂(g) In the reaction given above, the mixture of CO and H₂ is:

(a) natural gas

(b) water gas

(c) producer gas

(d) industrial gas

Answer: (b) water gas

Explanation: CO + H₂ (mixture) is called water gas or syngas. This reaction is steam reforming of methane at high temperature. Natural gas is methane itself. Producer gas is CO + N₂. Concept Tested: Water gas – CO + H₂ from steam reforming of methane

Q. 14.  To weld metals together, high temperature is required. Such a high temperature is obtained by burning:

(a) Acetylene in oxygen

(b) LPG in oxygen

(c) Methane in oxygen

(d) Acetylene in nitrogen

Answer: (a) Acetylene in oxygen

Explanation: Oxy-acetylene welding (burning C₂H₂ in O₂) produces a flame of approximately 3500 °C – the highest temperature achievable by combustion. This is sufficient to weld and cut metals. Methane or LPG produce lower temperatures. Concept Tested: Oxy-acetylene welding – highest temperature fuel-oxygen flame

NDA 2014-I

Q. 15.  Dihydrogen can be prepared on a commercial scale by the action of steam on hydrocarbons, when a mixture of CO and H₂ gas is formed. It is known as

(a) water gas

(b) producer gas

(c) industrial gas

(d) fuel gas

Answer: (a) water gas

Explanation: The reaction of steam with hydrocarbons (or carbon) at high temperature gives a mixture of CO and H₂, known as water gas (or synthesis gas / syngas): C + H₂O → CO + H₂. Producer gas is a mixture of CO and N₂. Concept Tested: Water gas = CO + H₂ mixture

NDA 2013-II

Q. 16.  Biogas consists of mainly

(a)  Methane

(b)  Ethane

(c)  Butane

(d)  Carbon dioxide

Answer: (a) Methane

Explanation: Biogas produced from organic waste (cow dung, agricultural waste) mainly consists of methane (CH₄, 55–70%) and carbon dioxide (CO₂, 30–40%). The major combustible component is methane. Concept Tested: Biogas composition – mainly methane

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