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Q1. Combustion of carbon produces:
Combustion is a chemical reaction in which a substance reacts with oxygen to produce heat and light. When carbon (like charcoal or diamond) burns in sufficient oxygen, it forms carbon dioxide (CO₂) and releases heat and light. For example: C + O₂ → CO₂ + heat + light. Carbon monoxide is formed only when oxygen is insufficient. Smoke is from incomplete combustion. So complete combustion of carbon gives CO₂ with heat and light.
Q2. A carbon compound with a double bond is called:
The suffix ‘-ene’ indicates a carbon-carbon double bond. Propene (C₃H₆) has the structure CH₃–CH=CH₂. Propanol is an alcohol (-OH group), propane is an alkane (single bonds only), propyne is an alkyne (triple bond). So a compound with a double bond is correctly called propene.
Q3. Unsaturated hydrocarbons generally burn with:
Unsaturated hydrocarbons (alkenes and alkynes) have a higher carbon to hydrogen ratio. They do not get enough oxygen for complete combustion because carbon atoms are more. The incomplete combustion produces unburnt carbon particles (soot) that glow yellow in the flame. For example, ethyne (acetylene) burns with a yellow sooty flame when air is limited. Blue flame indicates complete combustion (saturated hydrocarbons like methane).
Q4. Bromopentane contains which heteroatom?
A heteroatom is any atom other than carbon or hydrogen in an organic compound. Bromopentane (C₅H₁₁Br) contains the heteroatom bromine (Br). The name “bromo-” clearly indicates the presence of bromine. Oxygen would give “-ol” or “-al” etc., nitrogen would give “-amine”, chlorine would give “-chloro”. So bromine is correct.
Q5. Incomplete combustion results in formation of:
Incomplete combustion occurs when there is insufficient oxygen. Instead of forming carbon dioxide, carbon burns partially to form carbon monoxide (CO) and unburnt carbon particles (soot or carbon black). For example: 2C + O₂ → 2CO (insufficient oxygen) or C + O₂ → CO₂ (complete). Water may still form, but soot is the characteristic product of incomplete combustion. Carbon dioxide is from complete combustion.
Q6. A blue flame is obtained when fuel burns in:
A blue flame indicates complete combustion, which happens when there is sufficient or excess oxygen (oxygen-rich air). Complete combustion produces carbon dioxide and water, with no soot particles. The flame is blue and clean (like a Bunsen burner with air holes open). Oxygen-poor air gives a yellow sooty flame. Nitrogen and carbon dioxide do not support combustion.
Q7. Combustion of fuels mainly produces:
The primary purpose of burning fuels (like petrol, diesel, coal, natural gas) is to produce energy — specifically heat energy, and often light energy as well. This energy is used for cooking, heating, running engines, generating electricity, etc. Pollutants and smoke are unwanted byproducts, not the main product. Ash is produced from solid fuels but not from gaseous fuels. So energy is the main product.
Q8. A carbon compound with a triple bond is called:
The suffix ‘-yne’ indicates a carbon-carbon triple bond. Propyne (C₃H₄) has the structure CH₃–C≡CH. Propane has only single bonds, propene has a double bond, propanol is an alcohol. So propyne is correct for a compound with a triple bond.
Q9. The product formed when ethanol reacts with sodium metal is:
Ethanol (C₂H₅OH) contains an –OH group similar to water. It reacts with sodium metal to form sodium ethoxide (C₂H₅ONa) and hydrogen gas. The reaction is: 2C₂H₅OH + 2Na → 2C₂H₅ONa + H₂↑. This is similar to the reaction of sodium with water (2H₂O + 2Na → 2NaOH + H₂). Sodium acetate and water would come from reaction with acetic acid. Sodium chloride and ethanol is not a reaction. Sodium carbonate and oxygen is incorrect.
Q10. Petroleum is called a fossil fuel because it is formed from:
Fossil fuels (coal, petroleum, natural gas) are called so because they are formed from the remains (fossils) of dead plants and animals that lived millions of years ago. These remains were buried under layers of sediment and transformed by heat and pressure over geological time. Petroleum is not made from rocks, soil (though it is found in soil layers), or minerals (though associated with them). The key is fossils of living organisms.
Q11. Petroleum and natural gas were formed from:
Petroleum and natural gas are formed from the remains of tiny marine organisms (plankton, algae, and other sea creatures) that lived millions of years ago. These organisms sank to the ocean floor, were buried under sediments, and transformed by heat and pressure over time. Coal is formed from land plants. Volcanic rocks and coal beds are not the source. So marine plants and animals is correct.
Q12. Yellow flame indicates:
A yellow or orange flame indicates incomplete combustion due to insufficient oxygen. The yellow colour comes from unburnt carbon particles (soot) that get heated and glow. This is seen in a candle flame or a Bunsen burner with air holes closed. Complete combustion gives a blue flame. No combustion gives no flame. So yellow flame = incomplete combustion.
Q13. A flame is produced only when:
A flame is a region where combustion of gases takes place. Only substances that vaporise (turn into gas) during burning produce a flame. Solids like charcoal and metals like magnesium burn but do not vaporise easily, so they glow (red hot) but do not produce a flame. Liquids like kerosene vaporise first, then the vapours burn with a flame. But the direct answer: flame is produced only when gaseous substances burn.
Q14. Oil and gas get trapped in rocks because rocks are:
Petroleum and natural gas are found trapped in underground reservoir rocks that are porous (having tiny holes or pores) and permeable. The pores allow oil and gas to accumulate. Above these reservoir rocks is a non-porous cap rock that prevents the oil and gas from escaping. Rocks being smooth, hard, or magnetic has nothing to do with trapping oil and gas. Porosity is the key property.
Q15. Oxides of sulphur and nitrogen are:
Oxides of sulphur (SO₂, SO₃) and nitrogen (NO, NO₂) are major air pollutants. They are released when fossil fuels containing sulphur and nitrogen are burned. These oxides cause acid rain (by forming sulphuric and nitric acids), respiratory problems, and damage to buildings and plants. They are not catalysts (though they can participate in atmospheric reactions), not fertilisers (they harm soil), and not fuels (they do not burn to produce energy).
Q16. Coal and petroleum were formed from:
Coal and petroleum are fossil fuels formed from biomass — the remains of living organisms (plants and animals) that died millions of years ago. Coal comes mainly from land plants (trees, ferns) in swamps. Petroleum comes from marine organisms (plankton). Rocks, minerals, and lava are not the source materials. Biomass is the correct term for organic matter from living things.
Q17. Combustion of methane is an example of:
Combustion is a chemical reaction in which a substance combines with oxygen. In the combustion of methane (CH₄ + 2O₂ → CO₂ + 2H₂O), carbon and hydrogen gain oxygen — this is oxidation. Oxidation is defined as gain of oxygen or loss of hydrogen. Displacement reaction involves one element replacing another. Neutralisation is between acid and base. Reduction is loss of oxygen or gain of hydrogen. So combustion is oxidation.
Q18. Fuels used by us are mainly:
Most common fuels we use (coal, petrol, diesel, kerosene, natural gas, LPG, wood, biogas) are either carbon in elemental form (coal, charcoal) or compounds of carbon (hydrocarbons). They burn to release energy. Salts do not burn, metals (except magnesium, etc.) are not used as common fuels, and non-metals like oxygen do not burn (they support burning). So carbon or its compounds is correct.
Q19. Oxidation of alcohol involves:
Oxidation of an alcohol (like ethanol) involves gain of oxygen. For example, ethanol (C₂H₅OH) when oxidised becomes ethanal (CH₃CHO, an aldehyde) and further to ethanoic acid (CH₃COOH, a carboxylic acid). In these reactions, the alcohol gains oxygen atoms. Gain of hydrogen is reduction. Loss of oxygen is reduction. Loss of carbon is not typical oxidation. So gain of oxygen is correct.
Q20. Potassium permanganate is used as:
Potassium permanganate (KMnO₄) is a strong oxidising agent. It readily gives oxygen to other substances. In organic chemistry, it is used to oxidise alcohols to aldehydes or acids, and to test for unsaturation (purple colour disappears with alkenes). It is not a reducing agent (it does not accept oxygen), not an indicator (though it is coloured, it is not used as a pH indicator like litmus), and not a catalyst (it is consumed in the reaction). So oxidising agent is correct.
Q21. Black deposit on metal plate is due to:
When a metal plate is held over a flame (especially a yellow flame from incomplete combustion), a black deposit forms. This is unburnt carbon particles (soot) produced by incomplete combustion of carbon compounds. Sulphur deposits are yellow, nitrogen and oxygen do not form black deposits. So the black deposit is carbon (soot).
Q22. Blocking air holes of a stove results in:
Air holes in a stove supply oxygen for combustion. When air holes are blocked, less oxygen reaches the flame. This causes incomplete combustion, producing unburnt carbon particles (soot) that appear as a yellow flame and blacken utensils. Combustion still occurs (not no combustion). Clean flame comes from open air holes (blue flame). Fuel is wasted, not saved, because incomplete combustion produces less heat. So soot formation is correct.
Q23. Incomplete combustion wastes fuel because:
Incomplete combustion occurs when there is insufficient oxygen. Some fuel remains unburnt or is converted to carbon monoxide (which burns further if more oxygen is available) and soot. Because the fuel does not burn completely, less heat energy is released compared to complete combustion. This wastes fuel — you need to burn more fuel to get the same amount of heat. More heat is not produced (less heat is produced). Water formation is not waste. Less oxygen is used is a cause, not the waste itself.
Q24. Hexanal belongs to which functional group?
The suffix ‘-al’ in IUPAC nomenclature indicates an aldehyde functional group (-CHO). Hexanal has 6 carbons (hex-) with an aldehyde group. Ketones use ‘-one’, alcohols use ‘-ol’, carboxylic acids use ‘-oic acid’. So hexanal is an aldehyde.
Q25. A luminous flame is produced when:
A luminous flame (yellow, glowing) is produced when unburnt carbon particles (soot) are heated to high temperatures and glow. These particles are atoms of carbon (or small clusters) that emit light when hot. This happens in incomplete combustion. Molecules breaking, ions forming, or electrons being lost are part of combustion chemistry but do not directly explain the luminosity. The glow comes from hot solid carbon particles.
Q26. Ethanol burns to form:
Ethanol (C₂H₅OH) undergoes complete combustion when burned in sufficient oxygen. The products are carbon dioxide (CO₂) and water (H₂O). The balanced equation is: C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O. It does not produce hydrogen gas (H₂), only carbon and water (incomplete), or carbon monoxide (CO) and hydrogen (H₂). So CO₂ and H₂O is correct.
Q27. Initial flame in burning wood is due to:
When wood is heated, it first releases volatile substances (gases and vapours like methane, methanol, and other hydrocarbons) from the breakdown of cellulose and lignin. These volatile substances catch fire and produce the initial flame. Moisture evaporates but does not burn. Ash remains after burning. Fixed carbon (charcoal) burns later with a glow, not a flame. So volatile substances cause the initial flame.
Q28. Bacteria played a role in formation of petroleum by:
Millions of years ago, dead marine organisms (plankton, algae) sank to the ocean floor. Bacteria decomposed these organic remains in the absence of oxygen (anaerobic decomposition). Over time, the decomposed material was buried under sediments, and heat and pressure converted it into petroleum and natural gas. Bacteria did not burn, evaporate, or oxidise the remains (oxidation requires oxygen, which was absent). So decomposing remains is correct.
Q29. Fossil fuels are non-renewable because:
A non-renewable resource is one that cannot be replenished within a human lifetime. Fossil fuels (coal, petroleum, natural gas) take millions of years to form from the remains of dead organisms under high pressure and temperature. Once used up, they cannot be made again quickly. Burning easily, being expensive, or polluting the environment are not the reasons they are called non-renewable — the formation time is the key.
Q30. Number of structural isomers possible for pentane is:
Pentane (C₅H₁₂) has three structural isomers: (1) n-pentane — straight chain of 5 carbons; (2) isopentane (2-methylbutane) — 4-carbon chain with a methyl group on the second carbon; (3) neopentane (2,2-dimethylpropane) — 3-carbon chain with two methyl groups on the middle carbon. So the number is three.
Q31. Coal sometimes burns without flame because:
A flame is produced only when gaseous substances burn. Coal is mostly solid carbon. When coal burns, it does not vaporise easily; it undergoes combustion directly on the surface, glowing red hot without producing much flame. (Volatile matter in coal can produce some flame initially, but coke burns without flame). Coal does contain carbon (it is mostly carbon). Wet coal burns poorly. Burning too fast is not the reason. So it burns without flame because it does not produce combustible gases in large amounts.
Q32. Oxides of sulphur and nitrogen are formed by burning fuels containing:
When fuels containing sulphur (like coal, diesel) are burned, the sulphur combines with oxygen to form sulphur oxides (SO₂, SO₃). When fuels are burned at high temperatures (in vehicle engines), nitrogen from the air combines with oxygen to form nitrogen oxides (NO, NO₂). These oxides are pollutants. Carbon-only fuels (like charcoal) do not produce these oxides. Hydrogen gives water, oxygen is the oxidiser. So fuels containing nitrogen and sulphur (or high-temperature conditions) produce these oxides.
Q33. Cyclopentane is a:
The prefix ‘cyclo-‘ indicates a ring structure. Cyclopentane (C₅H₁₀) has five carbon atoms arranged in a closed ring. It is a cyclic compound (alicyclic, not aromatic). It is not aromatic (benzene is aromatic, cyclopentane is saturated). It is not branched (branched means a main chain with side groups). It is not straight chain (that would be pentane). So cyclic compound is correct.
Q34. Blackening of cooking vessels indicates:
Blackening (soot deposit) on cooking vessels occurs due to incomplete combustion, which happens when there is insufficient oxygen supply. In stoves, blocked air holes reduce oxygen flow, causing a yellow sooty flame that deposits unburnt carbon on utensils. Clean combustion (blue flame) does not blacken vessels. Proper air supply prevents blackening. High efficiency means less blackening. So blocked air holes cause blackening.
Q35. Cyclopentane contains how many carbon atoms?
The prefix ‘pent-‘ (or ‘penta’) means five. Cyclopentane has five carbon atoms arranged in a ring. The molecular formula is C₅H₁₀. Six carbons would be cyclohexane, three carbons cyclopropane, four carbons cyclobutane. So five is correct.
Q36. Structural isomers are possible for bromopentane because:
Structural isomers are compounds with the same molecular formula but different structural arrangements. Bromopentane (C₅H₁₁Br) has multiple isomers because the bromine atom can be attached to different carbon atoms (1-bromopentane, 2-bromopentane, 3-bromopentane) and also because the carbon chain can be branched. The existence of isomers does not require double bonds, cyclic structure, or aromaticity. The definition of isomerism is same formula, different structure.
Q37. Blue flame indicates:
A blue flame indicates complete combustion with sufficient oxygen supply. There are no unburnt carbon particles (soot), so the flame is clean and blue. Complete combustion produces maximum heat and is most efficient. Incomplete combustion gives a yellow flame. Low temperature would give a dim flame, not blue. Nitrogen does not affect flame colour (it is inert). So blue flame = complete combustion.
Q38. Coal formation involved:
Coal formed from dead land plants (trees, ferns) that accumulated in swamps millions of years ago (Carboniferous period). These plant remains were buried under layers of sediment and subjected to high pressure and temperature over millions of years. This process (coalification) gradually converted the plant matter into peat, then lignite, then bituminous coal, and finally anthracite. Chemical synthesis in a lab is artificial. Evaporation and sudden cooling are not involved.
Q39. Oil and gas were formed under:
Petroleum (oil) and natural gas formed from the remains of marine organisms buried under layers of sediment. Over millions of years, the increasing weight of overlying sediments created very high pressure (and high temperature) conditions. These conditions transformed the organic matter into oil and gas. Atmospheric pressure, no pressure, or low pressure would not be sufficient for this transformation. High pressure is essential.
Q40. Heating copper wire in flame gives characteristic colour because:
When a copper wire is heated in a flame, the copper atoms absorb energy and become excited. When they return to their ground state, they emit light of a characteristic colour (greenish-blue for copper). This is the principle of the flame test. Copper does not need to oxidise fully, melt, or burn to produce the colour. The colour comes from excited atoms (or ions) glowing. So copper atoms glow is correct.
Q41. Combustion of carbon compounds always requires:
Combustion is a chemical reaction in which a substance reacts with oxygen (oxidiser) to produce heat and light. Oxygen is essential for combustion. Without oxygen, combustion cannot occur. Carbon monoxide is a product of incomplete combustion, not a requirement. Hydrogen is a fuel, not a requirement. Nitrogen is inert and does not support combustion (it dilutes oxygen in air). So oxygen is always required.
Q42. Ethanoic acid belongs to which functional group?
Ethanoic acid (CH₃COOH) is also known as acetic acid. It contains the –COOH (carboxyl) group, which is the functional group of carboxylic acids. Alcohols have -OH, ketones have C=O between two carbons, aldehydes have -CHO. So carboxylic acid is correct. Ethanoic acid is the main component of vinegar.
Q43. Two properties of carbon responsible for a large number of compounds are:
The two key properties of carbon that lead to millions of compounds are: (1) Tetravalency — carbon can form four covalent bonds; (2) Catenation — carbon atoms can bond with other carbon atoms to form long chains, branches, and rings. Small size helps but is not the main reason. Density, conductivity, and acidity are not special properties of carbon. So tetravalency and catenation is correct.
Q44. Saturated hydrocarbons generally burn with:
Saturated hydrocarbons (alkanes like methane, ethane, propane, butane) have a lower carbon to hydrogen ratio. They burn completely in sufficient oxygen, producing a clean, blue flame with little or no smoke or soot. Unsaturated hydrocarbons (alkenes, alkynes) burn with a yellow sooty flame. So saturated hydrocarbons generally burn with a clean flame.
Q45. Coal is formed mainly from remains of:
Coal is formed from the remains of land plants — trees, ferns, and other vegetation — that grew in swamps millions of years ago (Carboniferous period). These plants died, accumulated in waterlogged swamps, and were buried under sediments. Over millions of years, heat and pressure converted them into coal. Marine organisms form petroleum and natural gas. Bacteria are decomposers. Animals contribute very little to coal formation.
Q46. Combustion is a type of:
Combustion is a chemical reaction in which a substance combines with oxygen, releasing heat and light. Since the substance gains oxygen, it is an oxidation reaction. Neutralisation is between acid and base. Displacement involves one element replacing another. Reduction is loss of oxygen or gain of hydrogen. So combustion is a type of oxidation reaction.
Q47. Yellow colour of candle flame is due to:
A candle flame is yellow because of incomplete combustion. The wax (hydrocarbon) does not burn completely due to limited oxygen, producing tiny unburnt carbon particles (soot). These carbon particles get heated in the flame and glow yellow. Oxygen and nitrogen are colourless gases. Sulphur burns with a blue flame. So the yellow colour comes from glowing carbon particles.
Q48. Ethanol is oxidised to form:
When ethanol (C₂H₅OH) is oxidised, it first forms ethanal (acetaldehyde, an aldehyde): C₂H₅OH → CH₃CHO + H₂O (loss of hydrogen). Further oxidation gives ethanoic acid (acetic acid, a carboxylic acid): CH₃CHO → CH₃COOH (gain of oxygen). Among the options, aldehyde is the immediate product of mild oxidation. Alkane would require reduction, ketone would require a different alcohol structure (secondary alcohol), carboxylic acid is the final product. For a JKBOSE level, the answer is often aldehyde (as the first oxidation product).
Q49. Combustion reactions release:
Combustion is defined as a chemical reaction that produces heat and light. For example, a burning candle gives both heat (warmth) and light (flame). Some combustion reactions (like burning charcoal) produce more heat than visible light, but light is still produced (glowing red). Combustion always releases both heat and light energy. It does not release only light, only smoke, or only heat. So heat and light is correct.