Exercise — Carbon and its Compounds

15 questions✓ Free · step-by-step

11 markNCERT Cl-10 Science, Exercise Q1
Ethane, with the molecular formula C₂H₆ has (a) 6 covalent bonds. (b) 7 covalent bonds. (c) 8 covalent bonds. (d) 9 covalent bonds.
Hint. Draw out CH₃-CH₃ and count every single bond, including the one joining the two carbons.
Step 1 — Draw the structure. Ethane is CH₃-CH₃ — two carbons joined by one C-C bond, with each carbon also bonded to 3 hydrogens.

Step 2 — Count the bonds. 1 C-C bond + 6 C-H bonds (3 on each carbon) gives 7 bonds in total, since every line in the structure is one shared electron pair.

✦ Answer: (b) 7 covalent bonds.
Where students slip. Counting only the 6 C-H bonds and forgetting the single C-C bond that joins the two carbons together — that bond is easy to overlook since it doesn't involve hydrogen.
21 markNCERT Cl-10 Science, Exercise Q2
Butanone is a four-carbon compound with the functional group (a) carboxylic acid. (b) aldehyde. (c) ketone. (d) alcohol.
Hint. The name itself ends in '-one' — match that suffix to its functional group.
Step 1 — Recall the suffix rule. The suffix '-one' indicates a ketone functional group (C=O within the carbon chain, not at the end).

Step 2 — Confirm with the structure. Butanone is CH₃-CO-CH₂-CH₃, with the C=O group on an internal carbon, which is why it's a ketone rather than an aldehyde (which would have -CHO at the end).

✦ Answer: (c) ketone.
Where students slip. Picking aldehyde — aldehydes also involve a C=O group, but always at the end of the chain (-CHO); butanone's C=O sits on an internal carbon, which is what makes it a ketone.
31 markNCERT Cl-10 Science, Exercise Q3
While cooking, if the bottom of the vessel is getting blackened on the outside, it means that (a) the food is not cooked completely. (b) the fuel is not burning completely. (c) the fuel is wet. (d) the fuel is burning completely.
Hint. Black soot is unburnt carbon — think about what produces that instead of a clean flame.
Step 1 — Identify the black deposit. The black deposit is soot — unburnt carbon particles.

Step 2 — Connect this to combustion. Soot forms when the fuel doesn't get enough oxygen to burn completely, since the carbon is then left behind unburnt instead of converting fully to CO₂.

✦ Answer: (b) the fuel is not burning completely.
Where students slip. Picking (d) — complete combustion gives a clean blue flame with no soot at all; blackening is specifically the sign of incomplete combustion, the opposite conclusion.
42 marksNCERT Cl-10 Science, Exercise Q4
Explain the nature of the covalent bond using the bond formation in CH₃Cl.
Hint. Carbon needs 4 bonds total — three go to hydrogen, and the fourth has to go somewhere.
Step 1 — Count carbon's bonding needs. Carbon has 4 valence electrons and needs to form 4 covalent bonds to complete its octet.

Step 2 — Assign the bonds in CH₃Cl. Three of carbon's bonds are single covalent bonds to three hydrogen atoms (each H sharing its one electron with carbon), and the fourth bond is a single covalent bond to chlorine, which has 7 valence electrons and needs just 1 more to complete its own octet.

Step 3 — Describe what each bond is. Each of these 4 bonds is a shared pair of electrons — one electron contributed by carbon, one by the bonding partner (H or Cl) — since it's exactly this sharing that gives carbon a full octet, each hydrogen a stable duet, and chlorine a full octet.

✦ Answer: In CH₃Cl, carbon forms 4 single covalent bonds — 3 to hydrogen atoms and 1 to chlorine — each bond being a shared pair of electrons that completes the octet (or duet, for hydrogen) of both atoms involved.
Where students slip. Describing the C-Cl bond as somehow different in kind from the C-H bonds — all four bonds around carbon here are ordinary single covalent bonds, just formed with different bonding partners.
54 marksNCERT Cl-10 Science, Exercise Q5
Draw the electron dot structures for (a) ethanoic acid. (b) H₂S. (c) propanone. (d) F₂.
Hint. For (b) and (d), count valence electrons first — sulphur and fluorine need very different numbers of bonds.
Step 1 — (a) Ethanoic acid, CH₃COOH. One carbon (with 3 H atoms) is singly bonded to a second carbon, which is double-bonded to one oxygen and singly bonded to an -O-H group.

Step 2 — (b) H₂S. Sulphur has 6 valence electrons and needs 2 more, so it forms one single bond to each of two hydrogen atoms (H-S-H), keeping 2 lone pairs.

Step 3 — (c) Propanone, CH₃COCH₃. The central carbon is double-bonded to oxygen and singly bonded to two separate -CH₃ groups.

Step 4 — (d) F₂. Each fluorine atom has 7 valence electrons and needs just 1 more; the two atoms share a single electron pair (F-F), each keeping 3 lone pairs.

✦ Answer: (a) CH₃-COOH with a C=O and C-O-H on the acid carbon (b) H-S-H with 2 lone pairs on S (c) CH₃-CO-CH₃ with C=O on the central carbon (d) F-F, single bond, 3 lone pairs on each F.
Where students slip. Giving H₂S a bent double-bond structure like CO₂ — sulphur here forms two single bonds to hydrogen (like water's H-O-H shape), not double bonds.
63 marksNCERT Cl-10 Science, Exercise Q6
What is an homologous series? Explain with an example.
Hint. Think about what stays the same (the functional group) and what changes by a fixed amount (the chain length) as you move through the series.
Step 1 — Define the term. A homologous series is a family of compounds with the same functional group, represented by a common general formula, where each successive member differs from the one before it by a -CH₂- unit.

Step 2 — Give an example. The alcohol series: methanol (CH₃OH), ethanol (C₂H₅OH), propanol (C₃H₇OH), butanol (C₄H₉OH) — each has one more -CH₂- unit than the last, and all share the -OH functional group.

Step 3 — Note what stays similar and what changes. Chemical properties stay similar across the series (since they're governed by the shared functional group), while physical properties like melting and boiling points show a gradual increase with molecular mass.

✦ Answer: A homologous series is a family of compounds sharing one functional group, each member differing from the next by a -CH₂- unit — e.g. methanol, ethanol, propanol, butanol, all sharing the -OH group with similar chemical but gradually changing physical properties.
Where students slip. Saying members of a homologous series have identical properties throughout — chemical properties stay similar because of the shared functional group, but physical properties (like boiling point) do change gradually with chain length.
73 marksNCERT Cl-10 Science, Exercise Q7
How can ethanol and ethanoic acid be differentiated on the basis of their physical and chemical properties?
Hint. For the chemical test, think about which of the two reacts with a carbonate/hydrogencarbonate.
Step 1 — Physical properties. Ethanol has a characteristic alcoholic smell and does not affect litmus. Ethanoic acid has a pungent, vinegar-like smell, turns blue litmus red, and can freeze into ice-like crystals in cold weather (around 290 K), which is why it's called glacial acetic acid.

Step 2 — Chemical test. Adding sodium carbonate or sodium hydrogencarbonate: ethanoic acid reacts to give brisk effervescence of CO₂ gas, while ethanol shows no reaction at all.

✦ Answer: Physically, ethanoic acid has a pungent smell and turns litmus red, while ethanol is odourless in that sense and neutral to litmus. Chemically, ethanoic acid fizzes with sodium carbonate/hydrogencarbonate (releasing CO₂), while ethanol does not react with them at all.
Where students slip. Relying only on smell to distinguish them — smell can be subjective and unreliable in an exam answer; the definitive test is the reaction (or lack of it) with a carbonate/hydrogencarbonate.
83 marksNCERT Cl-10 Science, Exercise Q8
Why does micelle formation take place when soap is added to water? Will a micelle be formed in other solvents such as ethanol also?
Hint. Ask what's special about water that makes soap's hydrocarbon tail want to hide from it — then ask whether ethanol shares that property.
Step 1 — Explain why micelles form in water. Soap has a hydrophilic ionic head and a hydrophobic hydrocarbon tail. In water, the tails avoid contact with the surrounding water molecules and cluster together in the interior, while the ionic heads stay on the outside in contact with water — this arrangement is a micelle.

Step 2 — Consider ethanol instead. The hydrocarbon tail of soap is reasonably soluble in ethanol (unlike in water), so there's no strong driving force pushing the tails to cluster away from an ethanol solvent.

Step 3 — State the conclusion. Since the tails don't need to hide from ethanol the way they do from water, the same water-style micelle (tails in, ionic heads out) would not form in ethanol.

✦ Answer: Micelles form in water because soap's hydrocarbon tails are hydrophobic and cluster away from water, leaving the ionic heads facing outward. In ethanol, the hydrocarbon tail dissolves reasonably well, so there's no such clustering, and a water-style micelle does not form.
Where students slip. Assuming micelles form the same way in any liquid soap is added to — micelle formation specifically depends on the solvent being unfavourable to the hydrocarbon tail, which is true of water but not of ethanol.
92 marksNCERT Cl-10 Science, Exercise Q9
Why are carbon and its compounds used as fuels for most applications?
Hint. Think about how much energy is released, how available the fuels are, and how easy they are to store and transport.
Step 1 — Energy released. Carbon and its compounds (like coal, petroleum and natural gas) release a large amount of heat and light energy on combustion.

Step 2 — Availability and practicality. They occur abundantly as fossil fuels, and are relatively easy to store, transport and burn in a controlled way for cooking, transport and industry.

✦ Answer: Carbon compounds release large amounts of energy on burning, are abundantly available as fossil fuels, and are convenient to store, transport and burn — which is why they are used as fuel for most everyday and industrial applications.
Where students slip. Focusing only on 'carbon burns and releases energy' without mentioning availability and ease of use — the question is really asking why carbon fuels specifically dominate practical use, not just why combustion releases energy in general.
103 marksNCERT Cl-10 Science, Exercise Q10
Explain the formation of scum when hard water is treated with soap.
Hint. Think about which ions in hard water react with soap's carboxylate part, and what that reaction produces.
Step 1 — Recall what makes water hard. Hard water contains dissolved calcium and magnesium salts.

Step 2 — Explain what happens when soap is added. Soap is a sodium (or potassium) salt of a long-chain fatty acid. The calcium and magnesium ions in hard water displace the sodium/potassium from the soap, forming calcium and magnesium salts of the fatty acid.

Step 3 — Describe the result. These calcium/magnesium fatty-acid salts are insoluble in water, forming the curdy white precipitate known as scum, since the soap used up this way produces no useful lather.

✦ Answer: Calcium and magnesium ions in hard water react with the soap, displacing sodium/potassium and forming insoluble calcium/magnesium salts of the fatty acid — this insoluble precipitate is the scum.
Where students slip. Describing scum as just 'soap not dissolving properly' — it's specifically a new insoluble compound (calcium/magnesium salt of the fatty acid) formed by a genuine chemical reaction with the hardness ions.
111 markNCERT Cl-10 Science, Exercise Q11
What change will you observe if you test soap with litmus paper (red and blue)?
Hint. Soap is made from a strong base and a weak acid — think about which one 'wins' in the resulting salt.
Step 1 — Recall what soap is made from. Soap is the sodium (or potassium) salt of a long-chain fatty acid — a strong base combined with a weak acid.

Step 2 — Determine its overall nature. Such a salt is mildly basic (alkaline) in solution.

Step 3 — State the litmus result. Since it is basic, soap turns red litmus blue, and has no effect on blue litmus (it stays blue).

✦ Answer: Red litmus turns blue; blue litmus stays blue — soap is basic (alkaline) in nature.
Where students slip. Assuming soap is neutral because it 'cleans' rather than 'reacts' — soap is a genuine chemical salt, and being formed from a strong base and weak acid, it is measurably basic, not neutral.
123 marksNCERT Cl-10 Science, Exercise Q12
What is hydrogenation? What is its industrial application?
Hint. This is the reaction that turns liquid vegetable oil into solid vegetable ghee.
Step 1 — Define hydrogenation. Hydrogenation is an addition reaction in which hydrogen gas is added to an unsaturated hydrocarbon (one with a C=C or C≡C bond), in the presence of a catalyst such as palladium or nickel, converting it into a saturated hydrocarbon.

Step 2 — Give the industrial application. Vegetable oils, which have long unsaturated carbon chains, are hydrogenated using a nickel catalyst to convert them into saturated fats (vegetable ghee/vanaspati), since saturated fats are solid at room temperature and store for longer than the liquid oil.

✦ Answer: Hydrogenation is the addition of hydrogen to unsaturated hydrocarbons using a catalyst (like nickel) to make them saturated. Industrially, it is used to convert vegetable oils into solid vegetable ghee (vanaspati).
Where students slip. Forgetting to mention the catalyst — the reaction doesn't proceed at a useful rate without one, which is why nickel or palladium is a necessary part of the definition, not an optional detail.
132 marksNCERT Cl-10 Science, Exercise Q13
Which of the following hydrocarbons undergo addition reactions: C₂H₆, C₃H₈, C₃H₆, C₂H₂ and CH₄.
Hint. Addition reactions are only possible where there's a double or triple bond to add across.
Step 1 — Classify each hydrocarbon. C₂H₆ (ethane), C₃H₈ (propane) and CH₄ (methane) are all alkanes — saturated, with only single bonds. C₃H₆ (propene) is an alkene (one C=C bond). C₂H₂ (ethyne) is an alkyne (one C≡C bond).

Step 2 — Apply the rule. Only unsaturated hydrocarbons (those with a double or triple bond) can undergo addition reactions, since there's a multiple bond to add across.

✦ Answer: C₃H₆ and C₂H₂ undergo addition reactions; C₂H₆, C₃H₈ and CH₄ do not, since they are saturated.
Where students slip. Including one of the saturated alkanes (like C₃H₈) — no matter how large a saturated hydrocarbon is, it has no double or triple bond for anything to add across.
142 marksNCERT Cl-10 Science, Exercise Q14
Give a test that can be used to differentiate between saturated and unsaturated hydrocarbons.
Hint. Think of a coloured reagent that fades instantly in the presence of a double or triple bond.
Step 1 — Choose the test reagent. Bromine water (orange-coloured) is added to the hydrocarbon sample and shaken.

Step 2 — Describe the result for each type. An unsaturated hydrocarbon decolourises the bromine water immediately, since bromine adds directly across its double or triple bond. A saturated hydrocarbon does not decolourise bromine water under these conditions, since it has no multiple bond for the addition reaction to happen on.

✦ Answer: Add bromine water to the sample — an unsaturated hydrocarbon decolourises it instantly (addition reaction), while a saturated hydrocarbon does not.
Where students slip. Assuming any reaction with bromine proves unsaturation — saturated hydrocarbons can react with bromine too, but only slowly and by substitution, requiring sunlight; the instant decolourisation without those conditions is what specifically signals an addition reaction with an unsaturated compound.
153 marksNCERT Cl-10 Science, Exercise Q15
Explain the mechanism of the cleaning action of soaps.
Hint. Structure your answer around the two ends of the soap molecule and what each one does.
Step 1 — Describe the soap molecule. A soap molecule has a long hydrophobic hydrocarbon tail and a hydrophilic ionic head.

Step 2 — Explain what happens around a dirt/oil droplet. The hydrophobic tails of many soap molecules dissolve into the oily dirt, while the hydrophilic heads remain oriented outward into the surrounding water, forming a spherical cluster called a micelle with the dirt trapped at its centre.

Step 3 — Explain how the dirt is removed. Because the micelle's outer surface is ionic and water-facing, the whole cluster (with the dirt inside) becomes dispersible in water; agitation (scrubbing, beating, machine action) helps free the dirt from the fabric, and rinsing then carries the micelles, and the dirt inside them, away.

✦ Answer: Soap's hydrocarbon tails bury themselves in oily dirt while its ionic heads face outward into water, forming micelles that trap the dirt at their centre. Agitation loosens the dirt from the fabric into these micelles, and rinsing washes the micelles — and the dirt with them — away.
Where students slip. Describing soap as simply 'dissolving' the dirt in water — oil doesn't dissolve in water at all; the cleaning works by trapping the dirt inside micelles that are themselves dispersible in water, which is a different mechanism from dissolving.

Solutions written by the tuition.in editorial team and checked against the NCERT Class 10 Science textbook, Reprint 2026-27 (jesc104.pdf) — five in-text question sets (13 questions total, not 18 as some older manifests claim) plus one end-of-chapter Exercise (15 questions, not 20). Unchanged by rationalisation.. Questions are referenced from the NCERT textbook for identification.

All exercises in Carbon and its Compounds