Where Mindful Learning Begins
Where Mindful Learning Begins
Class 10 Science NCERT Solutions Chapter 4 (CBSE 2026-27) — every in-text question, every embedded Activity question, and all 15 back-of-chapter Exercises on this one page, solved with the reasoning behind each answer.
Carbon and its Compounds moves from why carbon forms covalent bonds rather than ions, through catenation and tetravalency — the two properties that let carbon build millions of compounds — to saturated and unsaturated hydrocarbons, chains, branches, rings, homologous series and nomenclature, and finally the chemical properties (combustion, oxidation, addition and substitution) and everyday importance of ethanol, ethanoic acid, soaps and detergents. These NCERT solutions work through every Activity-based question, every electron-dot structure asked in the text, and the full 15-question Exercise set in detail, making this one of the most structure-heavy chapters in the chemistry portion of the Class 10 Science syllabus.
Carbon and its Compounds builds on the ionic bonding from Chapter 3 to introduce an entirely different kind of bond — the covalent bond — and shows why this one small, versatile element is the basis of millions of known compounds, including every living thing. It moves from the basic sharing of electrons in simple molecules like H2, Cl2, O2 and N2, to methane and the two special properties (catenation and tetravalency) that make carbon so prolific, to saturated and unsaturated hydrocarbons, homologous series, and systematic naming, and finally to the real chemistry — combustion, oxidation, addition and substitution reactions — and two commercially vital compounds, ethanol and ethanoic acid, ending with how soaps and detergents actually clean. Every question woven through the chapter is solved here, section by section, in the order the textbook presents it: the two "QUESTIONS" boxes after Section 4.1, the five after Section 4.2, and one each after Sections 4.3, 4.4 and 4.5, plus the questions embedded directly inside Activities and "Do You Know" boxes, and the full 15-question Exercise set at the end.
How carbon and other elements share electron pairs to form stable molecules, and why carbon compounds have low melting points and don't conduct electricity.
Chains, branches and rings of carbon atoms, saturated vs unsaturated compounds, functional groups, and the systematic naming of carbon compounds.
Combustion, oxidation, addition and substitution reactions; the properties of ethanol and ethanoic acid; and how soap micelles actually lift dirt away.
Carbon has 4 valence electrons and each oxygen atom has 6, needing 2 more to complete its octet. Carbon forms a double bond with each oxygen atom (sharing 2 electron pairs with each), which satisfies carbon's valency of 4 and completes the octet of both oxygen atoms.
Sulphur has 6 valence electrons and needs 2 more to complete its octet. In S8, the eight sulphur atoms are joined into a closed ring by single covalent bonds — each sulphur atom bonds to its two neighbouring sulphur atoms, sharing one electron pair with each, and keeps two lone pairs to complete its octet.
Pentane (C5H12) has three structural isomers:
(i) Catenation — carbon's unique ability to form strong bonds with other carbon atoms, creating long chains, branched chains, or rings.
(ii) Tetravalency — carbon has a valency of four, letting it bond with four other atoms (of carbon or of other elements such as hydrogen, oxygen, nitrogen, sulphur, or halogens), giving rise to an enormous variety of compounds.
Cyclopentane has the formula C5H10. Five carbon atoms are joined in a ring by single bonds; since each carbon uses 2 of its 4 valencies to bond with its two ring neighbours, the remaining 2 valencies on each carbon are satisfied by 2 hydrogen atoms — giving a five-membered ring of CH2 units.
(i) Ethanoic acid (CH3COOH):
(ii) Bromopentane (C5H11Br), e.g. 1-bromopentane:
Yes — structural isomers are possible for bromopentane, since the Br atom can be attached at different carbon positions along the chain, and the carbon chain itself can be branched differently.
(iii) Butanone (a four-carbon ketone):
(iv) Hexanal (a six-carbon aldehyde):
(i) CH3–CH2–Br → Bromoethane
(ii) H–CHO (a one-carbon aldehyde) → Methanal (formaldehyde)
(iii) A six-carbon chain with a triple bond between the fifth and sixth carbons → Hex-1-yne (commonly called hexyne)
Ethanol gains oxygen when it converts to ethanoic acid, in the presence of an oxidising agent such as alkaline potassium permanganate or acidified potassium dichromate:
Since oxidation is defined as the addition of oxygen to a substance, and ethanol gains an oxygen atom to become ethanoic acid, this is an oxidation reaction.
Air contains only about 21% oxygen, diluted by a large proportion of nitrogen and other gases that don't support combustion. Burning ethyne with pure oxygen instead of air ensures much more complete and efficient combustion, producing a hotter flame with enough heat for welding. A mixture of ethyne and air would burn cooler and less efficiently — not hot enough for welding.
Litmus/pH test: a carboxylic acid is acidic and turns blue litmus red; an alcohol is neutral and does not change litmus colour.
Sodium hydrogencarbonate test: add a pinch of sodium hydrogencarbonate (baking soda) to the sample. A carboxylic acid reacts with it to produce brisk effervescence (CO2 gas, confirmable by turning lime water milky); an alcohol shows no such reaction.
Oxidising agents are substances capable of adding oxygen to other substances (bringing about oxidation). Examples: alkaline potassium permanganate and acidified potassium dichromate, which oxidise alcohols to carboxylic acids.
No. Detergents work equally well in both hard and soft water — they do not form an insoluble precipitate (scum) with the calcium and magnesium ions in hard water — so they produce good foam regardless of water hardness. Since a detergent behaves identically in hard and soft water, it cannot be used to test for hardness. (Soap, on the other hand, forms scum in hard water but lathers freely in soft water, so soap can be used for this test.)
Agitation (beating, scrubbing, shaking) physically dislodges and separates the dirt particles from the fabric. Without it, oily dirt would remain loosely attached to the cloth even with soap present; the mechanical action helps break the dirt away from the fibres so the soap micelles can fully trap it in the water and it can be rinsed away.
Burn the substance. If it is a carbon compound, it will produce carbon dioxide gas on burning. This can be confirmed by passing the gas through lime water — lime water turning milky confirms the presence of CO2, showing the substance contains carbon.
Chlorine (atomic number 17, configuration 2,8,7) has 7 valence electrons and needs 1 more to complete its octet. Two chlorine atoms share one electron pair (a single covalent bond) to form Cl2, each contributing and retaining 3 lone pairs.
Oxygen has 6 valence electrons and needs 2 more to complete its octet. In water, oxygen forms a single covalent bond with each hydrogen atom, using 2 of its 6 valence electrons and retaining 2 lone pairs.
Nitrogen has 5 valence electrons and needs 3 more to complete its octet. In ammonia, nitrogen forms three single bonds, one with each of the three hydrogen atoms, retaining 1 lone pair.
Three carbon atoms are linked in a chain by single bonds; the remaining valencies are satisfied by hydrogen — the two end carbons each bond to 3 hydrogens, and the middle carbon bonds to 2 hydrogens.
In ethyne, each carbon is bonded to only one hydrogen atom, leaving 3 valencies per carbon unsatisfied. These are satisfied by a triple bond between the two carbon atoms.
Cyclohexane (C6H12) has six carbon atoms joined in a hexagonal ring by single bonds, with each carbon bonded to two hydrogen atoms to satisfy its remaining valencies.
Each successive pair (CH3OH → C2H5OH → C3H7OH → C4H9OH) differs by a fixed –CH2– unit, i.e. a difference of 14u in molecular mass each time (C = 12u + 2H = 2u).
Yes — since successive members differ by a fixed –CH2– unit and share similar chemical properties (due to the common –OH group), this family of alcohols is a homologous series.
General formula for alkanes: CnH2n+2. General formula for alkynes: CnH2n–2 (alkenes, given in the text, are CnH2n).
They are called fossil fuels because they were formed from the remains (fossils) of plants and animals that lived millions of years ago, buried and transformed by heat, pressure, and biological/geological processes over immense periods of time.
The yellow colour of a candle flame is due to incomplete combustion, which produces unburnt, glowing carbon particles (soot) within the flame. These hot carbon particles emit a yellow light, giving the flame its yellow colour — unlike a clean blue flame from complete combustion with enough oxygen.
Initially, the pink/purple colour of alkaline KMnO4 fades/disappears each time it is added drop by drop, since it is being consumed while oxidising ethanol to ethanoic acid. Once all the ethanol has fully reacted, any additional KMnO4 has nothing left to oxidise, so its colour persists — signalling that the reaction is complete.
In a hydrocarbon (non-polar) solvent, the orientation would be reversed compared to water. Since the hydrocarbon "tail" is soluble in the hydrocarbon solvent while the ionic "head" is not, the tails would point outward into the solvent, while the ionic (hydrophilic) heads would cluster together in the interior of the micelle, away from the non-polar solvent.
Answer: (b) 7 covalent bonds
Ethane (CH3–CH3) has 1 C–C bond + 6 C–H bonds (3 on each carbon) = 7 covalent bonds total.
Answer: (c) ketone — the "-one" suffix indicates a ketone.
Answer: (b) the fuel is not burning completely — incomplete combustion produces soot (unburnt carbon), which blackens the vessel.
In CH3Cl, carbon (4 valence electrons) forms four single covalent bonds: three with hydrogen atoms (each hydrogen sharing its one electron) and one with chlorine (which has 7 valence electrons and needs 1 more). Each bond consists of carbon sharing one electron with the other atom, and that atom sharing one electron back — a single shared pair of electrons. This gives carbon a complete octet (4 shared pairs = 8 electrons), while each hydrogen achieves a stable duplet and chlorine achieves a complete octet.
(a) Ethanoic acid (CH3COOH): the carboxyl carbon is double-bonded to one oxygen (C=O) and single-bonded to an –OH group; the methyl carbon has 3 hydrogens and is singly bonded to the carboxyl carbon.
(b) H2S: sulphur (6 valence electrons, needs 2 more) forms single bonds with two hydrogen atoms: H–S–H, retaining 2 lone pairs.
(c) Propanone (CH3–CO–CH3): the middle carbon is double-bonded to an oxygen (C=O) and singly bonded to two methyl groups on either side.
(d) F2: fluorine (7 valence electrons, needs 1 more) forms a single covalent bond between two fluorine atoms: F–F, each retaining 3 lone pairs.
A homologous series is a series of compounds in which the same functional group substitutes for hydrogen in a carbon chain, so successive members differ by a fixed –CH2– unit (14u in molecular mass) and share similar chemical properties determined by their common functional group.
Example: the alcohol series — methanol (CH3OH), ethanol (C2H5OH), propanol (C3H7OH), butanol (C4H9OH) — each member differs from the next by one –CH2– unit, and all share similar chemistry due to their common –OH functional group.
Physical: ethanol has a lower melting point (156K) and a mild pleasant odour; ethanoic acid has a higher melting point (290K, freezes in cold winters — hence "glacial acetic acid") and a pungent, vinegar-like smell.
Chemical: ethanoic acid is acidic (turns blue litmus red) and reacts with sodium hydrogencarbonate to give brisk CO2 effervescence; ethanol is neutral (no effect on litmus) and shows no reaction with sodium hydrogencarbonate.
Soap molecules have a hydrophilic (water-loving) ionic end and a hydrophobic (water-repelling) hydrocarbon tail. In water, the hydrophobic tails cluster together in the interior (away from water) while the ionic ends face outward into the water, forming a spherical cluster called a micelle — this minimises contact between the tails and water.
In ethanol, since ethanol can interact with/dissolve the hydrocarbon part of the soap molecule more readily than water can, soap tends to dissolve more uniformly rather than clustering into micelles as it does in water.
Carbon and most of its compounds release a large amount of heat and light energy on combustion in oxygen. Many carbon compounds (methane, ethanol, and hydrocarbons in coal and petroleum) are abundant, relatively easy to store and transport, and burn to give mainly carbon dioxide and water — making them efficient, high-energy fuel sources for most everyday and industrial applications.
Hard water contains dissolved calcium and magnesium salts. When soap (sodium/potassium salts of long-chain carboxylic acids) is added, these calcium and magnesium ions react with the soap to form insoluble calcium/magnesium salts of the fatty acids. This insoluble precipitate is called scum, and it forms instead of a good lather — meaning more soap needs to be used before proper foam forms.
Soap is basic in nature (a salt of a strong base like NaOH and a weak fatty acid), so it will turn red litmus paper blue, while it will have no effect on blue litmus paper (it remains blue).
Hydrogenation is the addition reaction in which unsaturated hydrocarbons (with double or triple bonds) add hydrogen in the presence of a catalyst (such as palladium or nickel) to form saturated hydrocarbons.
Industrial application: it is used to hydrogenate vegetable oils (which have unsaturated carbon chains) using a nickel catalyst, converting them into saturated fats such as vegetable ghee/margarine.
Addition reactions are given by unsaturated hydrocarbons (those with double or triple bonds). Of the given hydrocarbons, C3H6 (propene, has a double bond) and C2H2 (ethyne, has a triple bond) undergo addition reactions. C2H6, C3H8 and CH4 are saturated and do not.
Bromine water test: add a few drops of bromine water to the hydrocarbon sample. An unsaturated hydrocarbon rapidly decolourises the orange-brown bromine water (bromine adds across the double/triple bond), while a saturated hydrocarbon does not readily decolourise it.
Soap molecules have a hydrophilic (water-loving) ionic head and a hydrophobic (water-repelling) long hydrocarbon tail that is attracted to oil/grease. When soap is added to water containing oily dirt, the hydrocarbon tails attach to the oily dirt particles while the ionic heads remain oriented toward the surrounding water. This forms spherical clusters called micelles, with the oily dirt trapped at the centre and the ionic heads facing outward into the water — keeping the whole cluster (with the dirt inside) suspended as a stable emulsion rather than separating out.
When clothes are agitated (rubbed, beaten, or shaken), this further helps dislodge dirt from the fabric so it gets trapped in the micelles, and the dirt-laden micelles are then rinsed away with water, leaving the fabric clean.
Next up is Chapter 5 — Life Processes. Or explore the full chapter list, browse the Class 10 Science hub, or book a free demo class for personalised coaching.
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