Class 10 Science Chapter 4 Carbon and its Compounds NCERT Solutions 2026 PDF Download

Ans: Carbon (Z=6) has 4 valence electrons. Oxygen (Z=8) has 6. Carbon shares 2 electrons with one Oxygen and 2 electrons with another Oxygen to complete octets for all three atoms.
Structure: $O :: C :: O$ or $O = C = O$

Ans: 1. Catenation: The unique ability of carbon to form bonds with other carbon atoms, giving rise to large molecules (long chains, branched chains, and rings).
2. Tetravalency: With a valency of 4, carbon can bond with four other atoms of carbon or atoms of other monovalent elements like Hydrogen, Chlorine, etc.

Ans: Cyclopentane is a cyclic alkane with 5 carbon atoms bonded in a ring.
Formula: $C_5H_{10}$
Structure: 5 Carbon atoms in a pentagon shape, connected by single bonds. Each Carbon is bonded to 2 Hydrogen atoms.

Ans:

• Physical: Ethanol has a pleasant smell, while Ethanoic acid smells like vinegar (pungent). Ethanol's melting point is lower than Ethanoic acid.
• Chemical: Ethanoic acid reacts with Sodium Carbonate ($Na_2CO_3$) to release $CO_2$ gas (effervescence), whereas Ethanol does not react with carbonates.

Ans: Soap molecules have two ends: a hydrophilic (water-loving) ionic head and a hydrophobic (water-fearing) carbon tail.
1. When added to water, the hydrophobic tails attach to dirt/grease, and hydrophilic heads point outwards into the water.
2. This forms a structure called a Micelle.
3. Agitation pulls the dirt (trapped in the center of the micelle) into the water, washing it away.

Ans: Micelles form because the hydrocarbon chains of soap are hydrophobic (insoluble in water) and cluster together away from water, while the ionic heads are hydrophilic.
No, micelles will not form in ethanol because the hydrocarbon tail of soap is soluble in ethanol (organic solvent), so there is no need to form clusters to hide from the solvent.

Ans: Oxidising agents are substances capable of supplying oxygen to other substances or removing hydrogen from them. Example: Alkaline $KMnO_4$ (Potassium Permanganate) or Acidified $K_2Cr_2O_7$ (Potassium Dichromate) are used to oxidise alcohols to carboxylic acids.

Ans: Hard water contains Calcium ($Ca^{2+}$) and Magnesium ($Mg^{2+}$) salts. When soap (Sodium salt of fatty acid) reacts with these ions, it forms Calcium or Magnesium salts of fatty acids which are insoluble in water. This insoluble precipitate is called scum.

Ans: Isomerism is the phenomenon where compounds have the same molecular formula but different structural formulae.
Isomers of Butane:
1. n-Butane: Straight chain ($CH_3-CH_2-CH_2-CH_3$)
2. Iso-Butane: Branched chain ($CH_3-CH(CH_3)-CH_3$)

Ans: Covalent compounds have strong bonds within the molecule but weak intermolecular forces (Van der Waals forces) between different molecules. Little energy is required to break these weak forces, resulting in low melting/boiling points.

Ans: It is a series of compounds with the same functional group and similar chemical properties, where successive members differ by a $-CH_2$ unit.
Characteristics:
1. Similar chemical properties.
2. Gradation in physical properties (e.g., boiling point increases with mass).

Ans: Ethanol reacts with Sodium to produce Sodium Ethoxide and Hydrogen gas.
$2C_2H_5OH + 2Na \rightarrow 2C_2H_5ONa + H_2 \uparrow$

Ans: Sulphur atoms are arranged in a ring (crown shape). Each Sulphur atom shares 1 electron with the Sulphur on its left and 1 with the Sulphur on its right to complete its octet (6 valence + 2 shared).

Ans:

• Esterification: Reaction of Acid + Alcohol to form Ester (Sweet smelling).
  $CH_3COOH + C_2H_5OH \xrightarrow{Acid} CH_3COOC_2H_5 + H_2O$
• Saponification: Hydrolysis of Ester with a Base (NaOH) to form Soap and Alcohol.
  $CH_3COOC_2H_5 + NaOH \rightarrow CH_3COONa + C_2H_5OH$

Ans: 1. Litmus Test: Acid turns blue litmus red. Alcohol has no effect.
2. Sodium Bicarbonate Test: Add a pinch of $NaHCO_3$. Acid reacts to release bubbles of $CO_2$ (brisk effervescence). Alcohol does not react.

Ans: Unsaturated hydrocarbons add hydrogen in the presence of catalysts (Nickel/Palladium) to form saturated hydrocarbons.
$R_2C=CR_2 + H_2 \xrightarrow{Ni} R_2CH-CHR_2$
Use: It is used in the hydrogenation of vegetable oils (unsaturated fat) to form Vanaspati Ghee (saturated fat).

Ans: Detergents (ammonium or sulphonate salts) do not form insoluble precipitates (scum) with the Calcium and Magnesium ions present in hard water. They remain effective and lather well even in hard water, unlike soaps which get wasted forming scum.

Ans:
X: Ethanol ($C_2H_5OH$)
Y: Ethanoic Acid ($CH_3COOH$) - formed by oxidation of X.
Z: Ethyl Ethanoate ($CH_3COOC_2H_5$) - Ester formed by X + Y.

Ans: Hexanal is an aldehyde with 6 carbons.
Structure: $CH_3-CH_2-CH_2-CH_2-CH_2-CHO$.

Ans:
1. Forming $C^{4+}$ requires removing 4 electrons, which needs huge energy.
2. Forming $C^{4-}$ involves holding 10 electrons with only 6 protons, which is unstable due to repulsion.
Hence, carbon shares electrons.

Ans: Graphite. It is slippery because its layers can slide over each other (lubricant) and has free electrons (conductor).

Ans: Concentrated $H_2SO_4$ acts as a dehydrating agent. It removes water formed during the reaction, shifting the equilibrium forward to produce more ester.

Ans: Dehydration occurs. Ethanol loses a water molecule to form Ethene.
$C_2H_5OH \xrightarrow{Hot Conc. H_2SO_4} CH_2=CH_2 + H_2O$