NCERT Solutions for Class 10 Science Chapter 4 Carbon and its Compounds

Answer: Carbon has 4 valence electrons and Oxygen has 6 valence electrons. In CO₂, the central carbon atom shares two pairs of electrons with each of the two oxygen atoms to form double covalent bonds.

Structure: :O::C::O: (where each pair of dots represent shared valence electron pairs).

Answer: An S₈ molecule consists of eight sulphur atoms linked together in a ring-like (puckered crown) structure. Each sulphur atom shares one electron pair with two adjacent sulphur atoms to form a single covalent bond.

Answer: Pentane (C₅H₁₂) has 3 structural isomers:

1. n-pentane: CH₃–CH₂–CH₂–CH₂–CH₃

2. Isopentane (2-methylbutane): CH₃–CH(CH₃)–CH₂–CH₃

3. Neopentane (2,2-dimethylpropane): C(CH₃)₄

Answer:

1. Catenation: The unique ability of carbon to form strong covalent bonds with other carbon atoms to form long chains, branched chains, and closed rings.

2. Tetravalency: Carbon has four valence electrons, allowing it to bond with four other monovalent atoms or groups of atoms (such as Hydrogen, Oxygen, Nitrogen, Chlorine).

Answer: The conversion of ethanol (CH₃CH₂OH) to ethanoic acid (CH₃COOH) involves the removal of hydrogen atoms and addition of oxygen atoms using an oxidising agent like alkaline KMnO₄ or acidified K₂Cr₂O₇.

Equation: CH₃CH₂OH + 2[O] → CH₃COOH + H₂O

Answer: No, because detergents form lather readily with both soft and hard water without reacting with the Calcium (Ca²⁺) and Magnesium (Mg²⁺) ions present in hard water. To test water hardness, soap should be used instead, as it forms insoluble precipitate (scum) in hard water.

(a) 6 covalent bonds
(b) 7 covalent bonds
(c) 8 covalent bonds
(d) 9 covalent bonds

Correct Answer: (b) 7 covalent bonds (1 C–C single bond and 6 C–H single bonds).

(a) Carboxylic acid
(b) Aldehyde
(c) Ketone
(d) Alcohol

Correct Answer: (c) Ketone (–CO– group).

(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.

Correct Answer: (b) The fuel is not burning completely (Incomplete combustion releases unburnt carbon particles as soot).

Answer: A soap molecule consists of two parts:

1. A hydrophobic ionic tail (hydrocarbon chain) that dissolves in oil/grease.

2. A hydrophilic ionic head (–COONa⁺) that remains in contact with water.

When soap is mixed with dirty water containing grease, soap molecules cluster together with their hydrophobic tails facing inwards towards the oil droplets and hydrophilic heads facing outwards into water, forming structures called micelles. These micelles trap the dirt and float in water, allowing dirt to be washed away easily during rinsing.