Chapter 11 — Carbon and its Compounds: Multiple Choice Questions
Instructions: Each question carries 1 mark. Choose the best answer.
1. The valency of carbon in organic compounds is ______.
Answer
(a) 2 (b) 3 (c) 4 (d) 1
✅ Answer: (c) 4
ExplanationCarbon has 4 valence electrons and forms 4 covalent bonds (valency = 4). This tetravalency, along with catenation (ability to bond with other carbon atoms), makes carbon capable of forming millions of different compounds.
2. The general formula of alkanes is ______.
Answer
(a) CₙH₂ₙ (b) CₙH₂ₙ₊₂ (c) CₙH₂ₙ₋₂ (d) CₙHₙ
✅ Answer: (b) CₙH₂ₙ₊₂
Explanation
- Alkanes (saturated): CₙH₂ₙ₊₂ (e.g., CH₄, C₂H₆, C₃H₈)
- Alkenes (one double bond): CₙH₂ₙ (e.g., C₂H₄, C₃H₆)
- Alkynes (one triple bond): CₙH₂ₙ₋₂ (e.g., C₂H₂, C₃H₄)
3. Ethanol (C₂H₅OH) belongs to the functional group ______.
Answer
(a) Carboxylic acid (b) Aldehyde (c) Alcohol (d) Ether
✅ Answer: (c) Alcohol
ExplanationThe functional group –OH (hydroxyl group) characterises alcohols. Ethanol = ethyl alcohol = C₂H₅OH. Other functional groups: –COOH = carboxylic acid, –CHO = aldehyde, –CO– = ketone, –COO– = ester.
4. The IUPAC name of CH₄ is ______.
Answer
(a) Ethane (b) Propane (c) Methane (d) Butane
✅ Answer: (c) Methane
ExplanationCarbon chain naming: 1C = methane, 2C = ethane, 3C = propane, 4C = butane, 5C = pentane, 6C = hexane, 7C = heptane, 8C = octane. CH₄ has 1 carbon = methane.
5. The property of carbon to form long chains by bonding with itself is called ______.
Answer
(a) Isomerism (b) Catenation (c) Polymerisation (d) Hybridisation
✅ Answer: (b) Catenation
ExplanationCatenation is the unique ability of carbon atoms to bond with each other to form long chains (straight, branched) and rings. Combined with tetravalency, this gives rise to the enormous diversity of organic compounds. Silicon also shows catenation but to a much lesser extent.
6. Acetic acid (CH₃COOH) has the functional group ______.
Answer
(a) –OH (b) –CHO (c) –COOH (d) –CO–
✅ Answer: (c) –COOH
ExplanationThe carboxyl group (–COOH) is the functional group of carboxylic acids. Acetic acid (ethanoic acid) is CH₃COOH. It gives vinegar its sour taste and is a weak acid. The –COOH group makes these compounds acidic.
7. Saponification is the process of making ______.
Answer
(a) Plastics (b) Soaps (c) Medicines (d) Fuels
✅ Answer: (b) Soaps
ExplanationSaponification is the process by which fats/oils (esters) are hydrolysed by a strong base (NaOH or KOH) to produce soap (sodium/potassium salts of fatty acids) and glycerol.
Fat + NaOH → Soap + Glycerol
Sodium soaps are solid; potassium soaps are soft/liquid.
8. Which of the following is an unsaturated hydrocarbon?
Answer
(a) Methane (b) Ethane (c) Propane (d) Ethene
✅ Answer: (d) Ethene
ExplanationSaturated hydrocarbons (alkanes) contain only C–C single bonds. Unsaturated hydrocarbons contain at least one double (alkenes) or triple bond (alkynes). Ethene (C₂H₄) has a C=C double bond → unsaturated. Methane, ethane, propane are saturated alkanes.
9. Isomers are compounds with ______.
Answer
(a) same molecular formula, different structural formula (b) same structural formula, different molecular formula (c) same both molecular and structural formulas (d) different number of atoms
✅ Answer: (a) same molecular formula, different structural formula
ExplanationIsomers have the same molecular formula but different arrangements of atoms (structural formula), giving different physical and chemical properties. Example: n-butane and isobutane both have formula C₄H₁₀ but different structures.
10. The addition of bromine water is used to test for ______.
Answer
(a) Saturated hydrocarbons (b) Unsaturated hydrocarbons (c) Alcohols (d) Carboxylic acids
✅ Answer: (b) Unsaturated hydrocarbons
ExplanationBromine water (orange-brown) is decolourised by unsaturated compounds (alkenes, alkynes) due to addition reaction across the double/triple bond:
CH₂=CH₂ + Br₂ → CH₂Br–CH₂Br (colourless)
Saturated hydrocarbons do NOT decolourise bromine water. This is a standard test for unsaturation.
Quick Revision — Carbon Compounds
| Series | Formula | Bond | Example |
|---|
| Alkanes | CₙH₂ₙ₊₂ | C–C single | CH₄ (methane), C₂H₆ (ethane) |
| Alkenes | CₙH₂ₙ | C=C double | C₂H₄ (ethene) |
| Alkynes | CₙH₂ₙ₋₂ | C≡C triple | C₂H₂ (ethyne/acetylene) |
Functional Groups
| Group | Name | Example |
|---|
| –OH | Hydroxyl (alcohol) | CH₃OH (methanol) |
| –COOH | Carboxyl (carboxylic acid) | CH₃COOH (acetic acid) |
| –CHO | Aldehyde | HCHO (formaldehyde) |
| –CO– | Ketone | CH₃COCH₃ (acetone) |
| –NH₂ | Amino (amine) | CH₃NH₂ (methylamine) |
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