Ans: 1. Catenation: carbon atoms can bond with each other to form long chains, branches, and rings. 2. Tetravalency: carbon has 4 valence electrons and can form 4 covalent bonds with various elements like H, O, N, S, and Cl.

Ans: Soaps: sodium/potassium salts of fatty acids; ineffective in hard water (form scum); biodegradable. Detergents: ammonium/sulphonate salts; effective in hard water; may not be biodegradable. Both form micelles to remove dirt.

Ans: Saponification is the process of making soap by heating fat/oil with NaOH. CH₃COOH + NaOH → CH₃COONa + H₂O. The functional group in ethanoic acid is carboxylic acid (–COOH).

Ans: Isomers are compounds with the same molecular formula but different structural arrangements. Example: C₄H₁₀ → n-Butane (straight chain: C–C–C–C) and Isobutane (branched: C with 3 branches). They have different physical properties.

Ans: Carbon is called versatile because it forms an enormous number of compounds (over 3 million) due to: (1) Catenation: ability to form bonds with other carbon atoms — long chains, branched chains, rings. (2) Tetravalency: 4 valence electrons allowing 4 covalent bonds with various elements (H, O, N, S, halogens). Carbon compounds range from simple (CH₄) to complex (proteins, DNA) and form the basis of all life on Earth.

Ans: Saturated hydrocarbons (Alkanes): Contain only single bonds (C–C). General formula CₙH₂ₙ₊₂. Examples: Methane (CH₄), Ethane (C₂H₆). Burn with a clean blue flame (complete combustion — enough H relative to C). Unsaturated hydrocarbons: Contain at least one double (alkenes, C=C) or triple bond (alkynes, C≡C). Alkenes: CₙH₂ₙ, e.g., Ethene (C₂H₄). Alkynes: CₙH₂ₙ₋₂, e.g., Ethyne (C₂H₂). Burn with a sooty/yellow flame (incomplete combustion due to higher carbon content). Unsaturated compounds decolourise bromine water (addition reaction); saturated compounds do not.

Ans: A micelle is a spherical cluster formed when soap molecules surround a grease/oil droplet in water. Soap molecule structure: long non-polar (hydrophobic) hydrocarbon tail + ionic polar (hydrophilic) head (–COO⁻Na⁺). In water with grease: The tails insert into the grease droplet (like-dissolves-like), while the heads remain outside in water. This forms a spherical micelle with grease trapped inside and charged heads facing the water. The micelle is stable in water and is washed away during rinsing, taking the grease with it. This is how soap emulsifies and removes oily dirt.

Ans: Ethanoic acid (CH₃COOH) is the IUPAC name for acetic acid. It is present in vinegar (3–8% solution). Properties: (1) Melting point 290 K (17°C) — pure ethanoic acid is called glacial acetic acid (solidifies in winter). (2) Weak acid — partially ionises: CH₃COOH ⇌ CH₃COO⁻ + H⁺. (3) Reacts with alcohols to form esters (esterification). (4) Has a pungent sour smell. (5) Used as preservative in food (vinegar), manufacturing dyes, perfumes.

Ans: Hydrogen gas is evolved: 2C₂H₅OH + 2Na → 2C₂H₅ONa + H₂.

Ans: The general formula of alkenes is CₙH₂ₙ (for n = 2, 3, ...), e.g. ethene C₂H₄.

Ans: Pure ethanoic acid has a melting point of 290 K, so in cold weather it freezes into ice-like (glacier-like) crystals. For this reason it is called glacial acetic acid.

Ans: Butane has two isomers: n-butane, CH₃–CH₂–CH₂–CH₃ (straight chain), and isobutane (2-methylpropane), CH₃–CH(CH₃)–CH₃ (branched chain). Both have the molecular formula C₄H₁₀.

Ans: A = ethanol (C₂H₅OH). It reacts with sodium: 2C₂H₅OH + 2Na → 2C₂H₅ONa (B, sodium ethoxide) + H₂. On oxidation, A gives C = ethanoic acid (CH₃COOH). A and C undergo esterification to give D = ethyl ethanoate (CH₃COOC₂H₅), which has a sweet fruity smell.

Ans: A soap molecule has a hydrophilic head and a hydrophobic hydrocarbon tail. In water the tails attach to oily dirt and the heads face the water, forming micelles that surround the dirt; the micelles are pulled away in rinsing and the dirt is removed. In hard water, soap reacts with calcium and magnesium salts to form an insoluble, sticky scum, so much soap is wasted and cleaning is poor. Detergents are sodium salts of sulphonic acids or ammonium salts with chloride; their calcium and magnesium salts are soluble, so they do not form scum and work in hard water as well.

Ans: Ionic compounds: formed by transfer of electrons; hard crystalline solids; high melting and boiling points; soluble in water; conduct electricity when molten or dissolved. Covalent compounds: formed by sharing of electrons; mostly gases, liquids or soft solids; low melting and boiling points; generally insoluble in water but soluble in organic solvents; poor conductors. Carbon has four valence electrons; to get an octet it would have to gain or lose four electrons, which needs too much energy (C⁴⁻ or C⁴⁺ is unstable). So carbon shares its electrons and forms covalent bonds.