Carbon and Organic Chemistry Complete Study Notes with MCQ for WBPSC, SSC, UPSC & Railway Exams

Carbon and organic chemistry forms one of the most vital, high-yield sections of the General Science syllabus across all competitive examinations. Carbon’s unique atomic structure enables it to form millions of organic compounds, which govern vital biological processes, industrial materials, fuels, and modern pharmaceuticals. Mastering fundamental concepts such as hybridization, allotropy, functional group reactions, polymer chemistry, and biomolecules allows aspirants to solve direct factual questions as well as application-based chemical problems effortlessly.

For candidates preparing for WBCS, UPSC, SSC CGL/CHSL, Railway (RRB NTPC/JE), Banking, and State PSCs, organic chemistry consistently accounts for a significant portion of the General Science section. West Bengal aspirants should note local connections, such as the Haldia Petrochemicals industrial hub, historical chemical research from the Bose Institute and University of Calcutta, and GI-tagged organic products like Darjeeling Tea (rich in polyphenols and tannins). This guide provides a detailed, exam-focused study resource complete with chemical formulas, memory tricks, standard textbook references, and 20 unique practice MCQs.

➤ Hybridization & Shapes: sp³ (Tetrahedral, 109.5°), sp² (Trigonal planar, 120°), sp (Linear, 180°)
➤ Hardest Natural Substance: Diamond (sp³ hybridized, 3D covalent network, electrical insulator)
➤ Good Electrical Conductor Allotrope: Graphite (sp² hybridized, 2D hexagonal layers, free delocalised π electrons)
➤ General Formulas: Alkanes (C_nH_2n+2), Alkenes (C_nH_2n), Alkynes (C_nH_2n-2)
➤ Hückel’s Rule of Aromaticity: Planar, cyclic, fully conjugated ring containing (4n + 2) π electrons
➤ Distinguishing Aldehydes: Tollens' Test (Silver mirror) & Fehling's Test (Red precipitate of Cu₂O)
➤ Saponification Reaction: Ester + Base (NaOH) → Soap (Sodium salt of fatty acid) + Glycerol
➤ Vulcanisation of Rubber: Heating natural rubber with Sulphur to form disulfide cross-links for durability and elasticity

1. Fundamental Properties and Bonding of Carbon

Carbon (Atomic Number Z = 6, Mass Number A = 12, Electronic Configuration: 1s² 2s² 2p²) sits in Group 14 and Period 2 of the Periodic Table. Its unique ability to create millions of stable organic compounds comes down to two major properties: Tetravalency and Catenation.

A. Tetravalency and Covalent Bonding

Carbon has 4 valence electrons. To complete its octet, it shares electrons with other atoms through covalent bonds instead of gaining (C⁴⁻) or losing (C⁴⁺) four electrons, which would require an extreme amount of energy. Depending on how those electrons are shared, carbon undergoes three main types of hybridization:

B. Catenation

Catenation is the ability of carbon atoms to link with one another through strong covalent bonds to form long open chains (straight or branched) or closed rings. The C–C bond dissociation energy is exceptionally high at 348 kJ/mol. Down Group 14, catenation drops sharply: C >> Si > Ge ≈ Sn. Lead (Pb) shows no catenation at all.

C. Allotropes of Carbon

Allotropes are different physical forms of the same element that have distinct structures but share identical chemical properties. To learn more about atomic structures and nuclear properties, check out our guide on Atoms, Periodic Table & Radioactivity.

• Diamond: Rigid 3D tetrahedral network of sp³ carbon atoms. It is the hardest naturally occurring substance with a high refractive index of 2.42. It conducts heat well but is an electrical insulator because it has no free electrons.
• Graphite: Made of 2D hexagonal layers of sp² carbon atoms held together by weak van der Waals forces. Because the layers slide over each other easily, graphite feels soft and slippery. The fourth valence electron stays delocalized across the layers, making graphite a good conductor of electricity.
• Fullerenes (C₆₀ - Buckminsterfullerene): A cage-like spherical molecule shaped like a soccer ball. It consists of 20 hexagons and 12 pentagons made of sp² hybridized carbon atoms.
• Graphene: A single 2D layer of carbon atoms arranged in a hexagonal honeycomb lattice. It has extraordinary electrical conductivity, mechanical strength, and thermal conductivity.
• Amorphous Carbon: Non-crystalline, impure forms such as Coal, Charcoal, Lampblack, and Coke.

D. Isomerism in Organic Compounds

Isomers are compounds that share the exact same molecular formula but have different physical or chemical properties.

• Structural Isomerism:
  • Chain Isomerism: Difference in the arrangement of the carbon skeleton (e.g., n-butane and isobutane).
  • Position Isomerism: Difference in the location of a functional group, double bond, or substituent (e.g., Propan-1-ol and Propan-2-ol).
  • Functional Isomerism: Different functional groups altogether (e.g., Ethanol [CH₃CH₂OH] and Dimethyl ether [CH₃OCH₃]).
  • Metamerism: Unequal distribution of alkyl chains attached to a polyvalent heteroatom (e.g., Diethyl ether [C₂H₅–O–C₂H₅] and Methyl propyl ether [CH₃–O–C₃H₇]).
• Stereoisomerism:
  • Geometrical Isomerism (cis/trans): Results from restricted rotation around a C=C double bond. The cis-isomer places identical groups on the same side, while the trans-isomer puts them on opposite sides (e.g., Maleic acid [cis] vs. Fumaric acid [trans]).
  • Optical Isomerism: Chiral molecules lacking internal symmetry rotate plane-polarized light. Dextrorotatory (+ / d) rotates light to the right (clockwise); Levorotatory (− / l) rotates light to the left (counter-clockwise).

2. Hydrocarbons (Aliphatic & Aromatic)

Hydrocarbons are organic compounds built entirely out of carbon and hydrogen atoms. They fall into two main families: aliphatic (open-chain or non-aromatic rings) and aromatic compounds. For foundational physics principles related to motion governing energy transformation in these systems, visit Electric Current & Magnetic Effects.

A. Saturated Hydrocarbons (Alkanes)

• Physical Properties: Non-polar, insoluble in water, but readily soluble in organic solvents. Boiling point rises with molecular weight. Branching lowers the boiling point because it reduces the surface area for van der Waals forces.
• Wurtz Reaction: Alkyl halides react with sodium metal in dry ether to form higher symmetrical alkanes:
  2 R–X + 2 Na —(Dry Ether)→ R–R + 2 NaX
• Free Radical Halogenation: Methane reacts with chlorine under sunlight (hν):
  CH₄ + Cl₂ —(hν)→ CH₃Cl + HCl (continues step-by-step up to CCl₄)
• Combustion: Complete combustion produces CO₂ and H₂O with a large release of heat:
  CH₄ + 2 O₂ → CO₂ + 2 H₂O + Heat (890 kJ/mol)

B. Unsaturated Hydrocarbons (Alkenes & Alkynes)

• Addition Reactions of Alkenes:
  • Hydrogenation (Sabatier-Senderens): Alkene + H₂ —(Ni/Pt/Pd, 200°C)→ Alkane. Used industrially to turn vegetable oils into Vanaspati Ghee.
  • Markovnikov's Rule: When an unsymmetrical reagent (like HX) adds to an unsymmetrical alkene, the negative part (X⁻) binds to the carbon that has fewer hydrogen atoms.
  • Kharasch Effect (Anti-Markovnikov): Adding HBr in the presence of organic peroxides flips the outcome, attaching H to the carbon with fewer hydrogens.
  • Ozonolysis: Alkenes react with O₃ followed by Zn/H₂O treatment to break the double bond into aldehydes or ketones. This reaction helps pinpoint the exact location of double bonds.
• Acidity and Reactions of Alkynes:
  • Terminal alkynes (R–C≡C–H) display weak acidity because the sp-hybridized carbon holds 50% s-character, making it strongly electronegative. They react with ammoniacal AgNO₃ to form a white precipitate of silver acetylide.
  • Cyclic Polymerisation: Passing ethyne gas through a red-hot iron tube at 873 K yields Benzene (3 C₂H₂ → C₆H₆).

C. Aromatic Hydrocarbons (Benzene & Arenes)

• Hückel's Rule of Aromaticity: A compound qualifies as aromatic if it is cyclic, planar, fully conjugated, and contains (4n + 2) π electrons (where n = 0, 1, 2, 3...). Benzene has 6 π electrons (n = 1).
• Electrophilic Aromatic Substitution (EAS) of Benzene:
  • Nitration: Benzene + Conc. HNO₃ + Conc. H₂SO₄ → Nitrobenzene + H₂O.
  • Sulfonation: Benzene + Fuming H₂SO₄ (Oleum) → Benzenesulfonic acid.
  • Halogenation: Benzene + Cl₂ —(Anhyd. FeCl₃/AlCl₃)→ Chlorobenzene.
  • Friedel-Crafts Alkylation: Benzene + CH₃Cl —(Anhyd. AlCl₃)→ Toluene + HCl.
  • Friedel-Crafts Acylation: Benzene + CH₃COCl —(Anhyd. AlCl₃)→ Acetophenone.
• Directive Influence of Substituents:
  • Ortho/Para-directing (Activating groups): –OH, –NH₂, –OCH₃, –CH₃ (electron-donating through resonance or induction). Halogens (–F, –Cl, –Br) are o/p-directing but slightly deactivating.
  • Meta-directing (Deactivating groups): –NO₂, –COOH, –CHO, –CN, –SO₃H (electron-withdrawing).

3. Functional Groups and Organic Reactions

Functional groups are specific clusters of atoms within a molecule that determine its chemical reactivity, regardless of how long the rest of the carbon chain is.

A. Alcohols, Phenols, and Ethers

• Preparation & Oxidation of Alcohols:
  • Primary (1°) Alcohol —(KMnO₄ or K₂Cr₂O₇/H⁺)→ Aldehyde → Carboxylic Acid.
  • Secondary (2°) Alcohol —(CrO₃ or K₂Cr₂O₇/H⁺)→ Ketone (resists further mild oxidation).
  • Tertiary (3°) Alcohol —(KMnO₄/H⁺)→ Undergoes alkenic dehydration and C–C cleavage under forcing conditions.
• Lucas Test for Alcohol Distinction: Lucas Reagent = Anhydrous ZnCl₂ + Concentrated HCl.
  • 3° Alcohols: Instant cloudiness at room temperature.
  • 2° Alcohols: Cloudiness appears within 5 minutes.
  • 1° Alcohols: Remains clear at room temperature; requires heating to react.
• Ethers: Williamson's Synthesis: Alkyl halide + Sodium alkoxide → Ether + Sodium halide (R–X + R'–ONa → R–O–R' + NaX). Operates via an S_N2 mechanism.

B. Aldehydes and Ketones

• Nucleophilic Addition: The carbonyl carbon is electron-deficient due to the polar >C⁺=O⁻ double bond. It easily undergoes addition with HCN, NaHSO₃, Grignard reagents (RMgX), and alcohols.
• Tollens' Silver Mirror Test: Aldehydes reduce Tollens' reagent [Ammoniacal Silver Nitrate, [Ag(NH₃)₂]⁺] to metallic silver, coating the tube walls like a mirror. Ketones do not react.
• Fehling's Test: Heating aldehydes with Fehling's reagent (Fehling A: CuSO₄ + Fehling B: Alkaline Sodium Potassium Tartrate) yields a brick-red precipitate of Cuprous oxide (Cu₂O).
• Aldol Condensation: Aldehydes or ketones containing at least one α-hydrogen react in dilute NaOH to form β-hydroxy aldehydes (Aldols).
• Cannizzaro Reaction: Aldehydes with NO α-hydrogen (e.g., Formaldehyde HCHO, Benzaldehyde C₆H₅CHO) undergo self oxidation-reduction in concentrated KOH to form an alcohol and a carboxylate salt.

C. Carboxylic Acids and Nitrogen Compounds

• Acidity Trend: Trichloroacetic acid > Dichloroacetic acid > Chloroacetic acid > Formic acid > Acetic acid > Phenol > Water > Ethanol. Electron-withdrawing groups (–NO₂, –Cl) pull electron density to boost acidity, while electron-donating groups (–CH₃) weaken it.
• Esterification: Carboxylic acid + Alcohol —(Conc. H₂SO₄ catalyst)→ Ester + Water (A reversible reaction with a sweet fruity scent).
• Basic Character of Amines: In aqueous solutions, the basicity order for methyl-substituted aliphatic amines is: 2° > 1° > 3° > NH₃ ((CH₃)₂NH > CH₃NH₂ > (CH₃)₃N > NH₃).
• Carbylamine Test (Isocyanide Test): Heating primary (1°) amines with chloroform (CHCl₃) and ethanolic KOH produces an intensely foul-smelling alkyl/aryl isocyanide (R–NC). This test is exclusive to primary amines.
• Diazonium Salts: Benzene diazonium chloride (C₆H₅N₂⁺Cl⁻), prepared by treating aniline with NaNO₂ + HCl at 0–5°C (Diazotisation), serves as a versatile building block for Sandmeyer reactions, Gattermann reactions, and azo dye synthesis.

4. Biomolecules, Polymers, and Everyday Chemistry

A. Biomolecules

To study how biological building blocks integrate with metabolic processes and nutrition, review our detailed notes on Digestive System and Nutrition: Vitamins, Minerals, Balanced Diet as well as Mendelian Genetics, DNA/RNA, Heredity and Evolution Explained.

• Carbohydrates: Polyhydroxy aldehydes or ketones.
  • Monosaccharides: Simple sugars that cannot be broken down further by hydrolysis. E.g., Glucose (Aldohexose), Fructose (Ketohexose), Ribose (Pentose).
  • Disaccharides: Yield 2 monosaccharide units upon hydrolysis. Sucrose (Glucose + Fructose, linked by α-1,2-glycosidic bond; non-reducing invert sugar), Lactose (Glucose + Galactose; milk sugar), Maltose (Glucose + Glucose).
  • Polysaccharides: Long-chain polymers. Starch (plant energy store; mixture of amylose & amylopectin), Glycogen (animal storage in liver/muscles), Cellulose (plant cell structural walls; β-1,4-glycosidic linkages, indigestible by human enzymes).
• Proteins and Amino Acids: Polymers of α-amino acids joined by peptide bonds (–CO–NH–).
  • There are 20 standard amino acids; 10 essential amino acids must come directly from our diet (e.g., Leucine, Lysine, Valine, Tryptophan).
  • Structure: Primary (sequence of amino acids), Secondary (α-helix and β-pleated sheet via H-bonds), Tertiary (3D spatial folding), Quaternary (multi-subunit association).
  • Denaturation: Unfolding of 2° and 3° structures caused by heat, acid, or heavy metals without breaking the primary peptide bonds (e.g., boiling an egg, curdling milk).
• Nucleic Acids: Polynucleotides made of Nitrogenous base + Pentose sugar + Phosphate group.
  • DNA: Deoxyribose sugar + Bases (Adenine, Guanine, Cytosine, Thymine). Double-helix structure proposed by Watson and Crick (1953). A pairs with T (2 H-bonds); G pairs with C (3 H-bonds).
  • RNA: Ribose sugar + Bases (Adenine, Guanine, Cytosine, Uracil). Single-stranded molecule that directs protein synthesis (mRNA, tRNA, rRNA).
• Vitamins:
  • Fat-Soluble: Vitamins A (Retinol - Night blindness), D (Calciferol - Rickets), E (Tocopherol - Infertility), K (Phylloquinone - Delayed blood clotting).
  • Water-Soluble: Vitamin C (Ascorbic acid - Scurvy), Vitamin B-Complex (B₁ Thiamine - Beriberi, B₂ Riboflavin - Cheilosis, B₃ Niacin - Pellagra, B₁₂ Cyanocobalamin - Pernicious anemia [contains Cobalt]).

B. Polymers

High-molecular-mass macromolecules created by linking small repeating monomer units together.

C. Chemistry in Everyday Life

• Cleansing Agents (Soaps vs Synthetic Detergents):
  • Soaps: Sodium or potassium salts of long-chain fatty acids (e.g., Sodium stearate C₁₇H₃₅COONa). Prepared by Saponification (Fat + NaOH → Soap + Glycerol). They fail in hard water because they react with Ca²⁺ and Mg²⁺ to form an insoluble precipitate (scum).
  • Detergents: Sodium salts of long-chain alkyl benzene sulphonates or alkyl sulphates. They clean effectively in both soft and hard water. Non-biodegradable branched detergents can accumulate in water bodies, causing pollution.
  • Micelle Formation: Soap molecules possess a hydrophobic hydrocarbon tail (grease-loving) and a hydrophilic ionic head (–COO⁻Na⁺, water-loving). In water, they group into spherical micelles above the Critical Micelle Concentration (CMC), trapping oil droplets in the core.
• Medicines and Pharmaceuticals:
  • Antipyretics: Lower high body temperature during fevers (e.g., Paracetamol, Aspirin).
  • Analgesics: Relieve pain. Divided into Non-narcotic (Aspirin, Ibuprofen, Paracetamol) and Narcotic/Opioid (Morphine, Codeine, Heroin).
  • Antiseptics vs Disinfectants: Antiseptics are safe for living tissues (e.g., Dettol [Chloroxylenol + Terpineol], Tincture of Iodine [2-3% I₂ in alcohol-water], Bithional in soap). Disinfectants are used on non-living objects (e.g., 1% Phenol solution, Chlorine 0.2-0.4 ppm). Notice: 0.2% Phenol acts as an antiseptic, whereas 1% Phenol acts as a disinfectant!
  • Antibiotics: Substances produced by microorganisms to destroy or stop bacteria. Alexander Fleming discovered Penicillin (1928) from Penicillium notatum. Broad-spectrum antibiotics (Chloramphenicol, Ampicillin) treat both Gram-positive and Gram-negative bacterial infections.
  • Antacids: Neutralize excess stomach acid (HCl). E.g., Sodium hydrogen carbonate (baking soda), Magnesium hydroxide [Mg(OH)₂ / Milk of Magnesia], Ranitidine, Cimetidine.

For more practice and complete coverage across disciplines, check out our recent guides on Sound: Nature, Speed, Echo, SONAR, Five-Year Plans, NITI Aayog & Finance Commission, and Gandhian Era: Non-Cooperation, Civil Disobedience, Quit India Movement.

Top 20 Unique Exam-Oriented Practice MCQs

Q1. A hydrocarbon molecule contains two sp³-hybridized carbon atoms and two sp-hybridized carbon atoms. Which of the following IUPAC names fits this description?
(a) But-2-ene
(b) But-1-yne
(c) Buta-1,3-diene
(d) Cyclobutane

Answer: (b) – But-1-yne has the formula CH₃–CH₂–C≡CH. The CH₃– and –CH₂– carbons are sp³ hybridized (4 single bonds), while the –C≡CH carbons are sp hybridized (triple bond).

Q2. Why is graphite soft and slippery, whereas diamond is exceptionally hard, despite both consisting solely of pure carbon?
(a) Graphite has sp³ hybridization while diamond has sp² hybridization
(b) Graphite consists of 2D hexagonal layers held by weak van der Waals forces, while diamond forms a rigid 3D tetrahedral network
(c) Diamond contains ionic bonds while graphite contains metallic bonds
(d) Graphite contains amorphous carbon impurities

Answer: (b) – Graphite forms planar hexagonal layers that slide over each other easily due to weak intermolecular forces. Diamond features a continuous 3D network of covalent bonds.

Q3. Buckminsterfullerene (C₆₀) features a spherical truncated icosahedron shape. How many hexagonal and pentagonal carbon rings make up this molecule?
(a) 12 Hexagons and 20 Pentagons
(b) 20 Hexagons and 12 Pentagons
(c) 14 Hexagons and 8 Pentagons
(d) 18 Hexagons and 12 Pentagons

Answer: (b) – The spherical C₆₀ fullerene structure contains exactly 20 hexagonal rings and 12 pentagonal rings.

Q4. Which of the following compounds displays functional isomerism with Ethanol (CH₃CH₂OH)?
(a) Methanol (CH₃OH)
(b) Dimethyl Ether (CH₃OCH₃)
(c) Propan-1-ol (CH₃CH₂CH₂OH)
(d) Ethanal (CH₃CHO)

Answer: (b) – Ethanol (an alcohol) and Dimethyl ether (an ether) share the molecular formula C₂H₆O but belong to different functional group classes.

Q5. What compound forms when Ethyne (C₂H₂) gas is passed through a red-hot iron tube at 873 K?
(a) Ethene
(b) Cyclohexane
(c) Benzene
(d) Toluene

Answer: (c) – Cyclic trimerization of three ethyne molecules over a red-hot iron tube at 873 K produces Benzene (3 C₂H₂ → C₆H₆).

Q6. When Propene (CH₃–CH=CH₂) reacts with HBr in the presence of benzoyl peroxide, what is the major product obtained?
(a) 2-Bromopropane
(b) 1-Bromopropane
(c) 1,2-Dibromopropane
(d) Propane

Answer: (b) – Peroxides trigger Anti-Markovnikov addition (Kharasch effect), attaching the bromine atom to the terminal carbon to form 1-Bromopropane.

Q7. An unknown organic liquid 'X' reacts with metallic sodium to release H₂ gas, but shows no cloudiness when mixed with Lucas reagent at room temperature until heated. What is 'X'?
(a) 2-Methylpropan-2-ol (3° Alcohol)
(b) Propan-2-ol (2° Alcohol)
(c) Propan-1-ol (1° Alcohol)
(d) Phenol

Answer: (c) – Primary alcohols react with sodium metal to evolve hydrogen gas, but they do not form an alkyl chloride turbidity with Lucas reagent at room temperature.

Q8. Which aldehyde undergoes the Cannizzaro reaction when treated with concentrated aqueous KOH solution?
(a) Acetaldehyde (CH₃CHO)
(b) Propionaldehyde (CH₃CH₂CHO)
(c) Benzaldehyde (C₆H₅CHO)
(d) Acetone (CH₃COCH₃)

Answer: (c) – Benzaldehyde lacks α-hydrogens on the carbon adjacent to the carbonyl group, causing it to undergo self-redox (Cannizzaro reaction) to yield benzyl alcohol and potassium benzoate.

Q9. What precipitate forms when an aldehyde is warmed with Fehling's reagent?
(a) Black precipitate of Silver metal
(b) Brick-red precipitate of Cuprous Oxide (Cu₂O)
(c) Yellow precipitate of Lead Iodide
(d) White precipitate of Copper Sulfate

Answer: (b) – Aldehydes reduce Cu²⁺ ions in Fehling's solution to Cu⁺ ions, resulting in a brick-red precipitate of Cuprous oxide (Cu₂O).

Q10. Heating a primary amine with Chloroform (CHCl₃) and alcoholic KOH produces an extremely offensive odor. What substance causes this smell?
(a) Alkyl Cyanide (R–CN)
(b) Alkyl Isocyanide (R–NC)
(c) Nitroalkane (R–NO₂)
(d) Alkyl Chloride (R–Cl)

Answer: (b) – The Carbylamine test converts 1° amines into carbylamines (isocyanides, R–NC), which emit an intensely foul smell.

Q11. Which carboxylic acid exhibits strong reducing properties and can reduce Tollens' reagent, unlike typical carboxylic acids?
(a) Acetic acid (CH₃COOH)
(b) Formic acid (HCOOH)
(c) Benzoic acid (C₆H₅COOH)
(d) Oxalic acid (HOOC–COOH)

Answer: (b) – Formic acid contains both a carboxyl group (–COOH) and an aldehyde-like hydrogen atom (H–C=O), allowing it to reduce Tollens' reagent to a silver mirror.

Q12. What glycosidic linkage connects the monosaccharide units in Cellulose, rendering it indigestible by human digestive enzymes?
(a) α-1,4-glycosidic bond
(b) β-1,4-glycosidic bond
(c) α-1,6-glycosidic bond
(d) α-1,2-glycosidic bond

Answer: (b) – Cellulose consists of linear chains of D-glucose linked by β-1,4-glycosidic bonds. Humans lack the cellulase enzyme required to break β-linkages.

Q13. Which water-soluble vitamin contains the metallic element Cobalt and causes Pernicious Anemia when deficient?
(a) Vitamin B₁ (Thiamine)
(b) Vitamin B₆ (Pyridoxine)
(c) Vitamin B₁₂ (Cyanocobalamin)
(d) Vitamin C (Ascorbic Acid)

Answer: (c) – Vitamin B₁₂ (Cyanocobalamin) contains a cobalt ion complexed within its structure. Deficiencies impair red blood cell maturation.

Q14. Natural rubber is a linear polymer made of which monomer unit?
(a) Chloroprene
(b) Isoprene (2-methyl-1,3-butadiene)
(c) Styrene
(d) Acrylonitrile

Answer: (b) – Natural rubber is a polymer of Isoprene (cis-1,4-polyisoprene).

Q15. Heating natural rubber with Sulphur to improve its elasticity, tensile strength, and heat resistance is known as what process?
(a) Vulcanisation
(b) Saponification
(c) Carbonisation
(d) Hydrogenation

Answer: (a) – Vulcanisation involves heating natural rubber with Sulphur (3–5%) to form cross-linking disulfide bridges between polymer chains.

Q16. Teflon, a popular non-stick polymer coating for cookware, is synthesized from which monomer?
(a) Vinyl Chloride
(b) Tetrafluoroethene
(c) Styrene
(d) Hexamethylenediamine

Answer: (b) – Teflon (Polytetrafluoroethylene / PTFE) is made by addition polymerization of Tetrafluoroethene (CF₂=CF₂).

Q17. Which of the following is a condensation copolymer made from Phenol and Formaldehyde?
(a) PVC
(b) Terylene
(c) Bakelite
(d) Nylon 6,6

Answer: (c) – Bakelite is a cross-linked thermosetting polymer formed by reacting Phenol with Formaldehyde in the presence of an acid or base catalyst.

Q18. Why do synthetic detergents clean effectively in hard water, whereas traditional soaps fail?
(a) Detergents are basic while soaps are acidic
(b) Detergents form soluble calcium and magnesium salts, while soaps form insoluble scum
(c) Detergents contain no hydrocarbon chains
(d) Detergents decompose hard water ions into gases

Answer: (b) – The calcium and magnesium salts of alkyl benzene sulphonates (detergents) stay soluble in water, preventing the formation of sticky scum.

Q19. Dettol is a widely used antiseptic solution. What are its two main active chemical ingredients?
(a) Chloroxylenol and Terpineol
(b) Phenol and Iodine
(c) Bithional and Ethanol
(d) Formic acid and Formaldehyde

Answer: (a) – Dettol is an antiseptic formulation made of Chloroxylenol and Terpineol dissolved in an alcohol-water mixture.

Q20. Which nitrogenous base is present in RNA but absent in DNA?
(a) Adenine
(b) Thymine
(c) Uracil
(d) Cytosine

Answer: (c) – Uracil (U) takes the place of Thymine (T) in RNA molecules. DNA contains Adenine, Guanine, Cytosine, and Thymine.

Summary & Exam Focus Points

To score high marks in Chemistry questions on competitive exams like WBCS, SSC, UPSC, and Railways, candidates should focus on five core topics: First, understand carbon hybridization (sp³, sp², sp), bond angles, and structural differences between Diamond and Graphite. Second, memorize general formulas for alkanes, alkenes, alkynes, and Hückel’s (4n+2) rule for aromaticity. Third, learn the key identifying tests for functional groups—especially Tollens' and Fehling's tests for aldehydes, Lucas test for alcohols, and the Carbylamine test for 1° amines. Fourth, memorize the exact monomer pairs for major polymers (Nylon 6,6, Terylene, Bakelite, Teflon, Neoprene). Finally, review practical chemistry applications including soap vs detergent action, micelle formation, antiseptics, and vitamin deficiency conditions.

Reference: NCERT Class XI & XII Chemistry (Units on Organic Chemistry, Hydrocarbons, Biomolecules, Polymers, and Chemistry in Everyday Life).