Hydrocarbons MCQs – Alkanes Alkenes Alkynes Class 11
Hydrocarbons MCQs – Alkanes, Alkenes & Alkynes (Class 11 Chemistry)
Course: CBSE Class 11 Chemistry – MCQs with Answers and Explanations
Section: Organic Chemistry – MCQ Titles
The following 50 Multiple Choice Questions (MCQs) are strictly based on the NCERT chapter “Hydrocarbons”. The questions are arranged section-wise to cover alkanes, alkenes, and alkynes, with clear, concept-clearing explanations, making them ideal for CBSE Class 11 board exam preparation.
Section A: Introduction to Hydrocarbons
1. Hydrocarbons are organic compounds containing only
A. carbon and oxygen
B. carbon and hydrogen
C. hydrogen and nitrogen
D. carbon and nitrogen
Answer: B
Explanation: Hydrocarbons consist exclusively of carbon and hydrogen atoms.
2. Which of the following is NOT a hydrocarbon?
A. Methane
B. Ethene
C. Ethanol
D. Ethyne
Answer: C
Explanation: Ethanol contains oxygen, so it is not a hydrocarbon.
3. Hydrocarbons are classified mainly into
A. acids and bases
B. saturated and unsaturated
C. aliphatic and aromatic only
D. ionic and covalent
Answer: B
Explanation: Based on presence or absence of multiple bonds.
Section B: Alkanes (Paraffins)
4. Alkanes are also known as
A. olefins
B. alkynes
C. paraffins
D. aromatics
Answer: C
Explanation: Alkanes are less reactive, hence called paraffins.
5. General formula of alkanes is
A. CₙHₙ
B. CₙH₂ₙ
C. CₙH₂ₙ₋₂
D. CₙH₂ₙ₊₂
Answer: D
Explanation: Saturated hydrocarbons follow CₙH₂ₙ₊₂.
6. Hybridisation of carbon in alkanes is
A. sp
B. sp²
C. sp³
D. dsp²
Answer: C
Explanation: Alkanes contain only single bonds.
7. Shape of methane molecule is
A. square planar
B. linear
C. trigonal planar
D. tetrahedral
Answer: D
Explanation: sp³ hybridisation gives tetrahedral geometry.
8. Which reaction is characteristic of alkanes?
A. Addition
B. Substitution
C. Elimination
D. Polymerisation
Answer: B
Explanation: Alkanes undergo free-radical substitution reactions.
9. Chlorination of methane in sunlight is an example of
A. electrophilic substitution
B. nucleophilic substitution
C. free radical substitution
D. addition reaction
Answer: C
Explanation: UV light initiates free radicals.
10. Which alkane shows maximum branching?
A. n-Butane
B. Isobutane
C. Neopentane
D. Propane
Answer: C
Explanation: Neopentane is highly branched.
Section C: Alkenes (Olefins)
11. Alkenes are unsaturated hydrocarbons containing
A. only single bonds
B. double bond
C. triple bond
D. aromatic ring
Answer: B
Explanation: Alkenes contain at least one C=C bond.
12. General formula of alkenes is
A. CₙH₂ₙ₊₂
B. CₙH₂ₙ
C. CₙH₂ₙ₋₂
D. CₙHₙ
Answer: B
Explanation: One double bond reduces two hydrogen atoms.
13. Hybridisation of carbon in ethene is
A. sp
B. sp²
C. sp³
D. dsp²
Answer: B
Explanation: Double bond requires sp² hybridisation.
14. Shape of ethene molecule is
A. tetrahedral
B. linear
C. trigonal planar
D. pyramidal
Answer: C
Explanation: sp² hybridised carbon gives planar structure.
15. Which reaction is typical of alkenes?
A. Substitution
B. Addition
C. Oxidation only
D. Neutralisation
Answer: B
Explanation: Alkenes readily undergo addition reactions.
16. Bromine water test is used to detect
A. alkanes
B. alkenes
C. alkynes
D. aromatics
Answer: B
Explanation: Alkenes decolourise bromine water.
17. Markovnikov’s rule is applicable to
A. alkanes
B. alkenes
C. alkynes
D. aromatics
Answer: B
Explanation: It explains orientation of addition to unsymmetrical alkenes.
18. According to Markovnikov’s rule, hydrogen adds to carbon with
A. more alkyl groups
B. less hydrogen atoms
C. more hydrogen atoms
D. higher electronegativity
Answer: C
Explanation: Hydrogen attaches to carbon already rich in hydrogen.
19. Which alkene shows geometrical isomerism?
A. Ethene
B. Propene
C. But-2-ene
D. Methene
Answer: C
Explanation: Restricted rotation around C=C causes cis-trans isomerism.
20. Which reagent causes polymerisation of alkenes?
A. Dilute acids
B. Heat and catalyst
C. Alkali
D. Water
Answer: B
Explanation: Heat and catalysts help alkene polymerisation.
Section D: Alkynes (Acetylenes)
21. Alkynes contain
A. single bond
B. double bond
C. triple bond
D. aromatic ring
Answer: C
Explanation: Alkynes have at least one C≡C bond.
22. General formula of alkynes is
A. CₙH₂ₙ₊₂
B. CₙH₂ₙ
C. CₙH₂ₙ₋₂
D. CₙHₙ
Answer: C
Explanation: Two degrees of unsaturation reduce hydrogen count.
23. Hybridisation of carbon in ethyne is
A. sp
B. sp²
C. sp³
D. dsp
Answer: A
Explanation: Triple bond requires sp hybridisation.
24. Shape of ethyne molecule is
A. tetrahedral
B. trigonal planar
C. bent
D. linear
Answer: D
Explanation: sp hybridisation gives linear geometry.
25. Ethyne burns with a
A. non-luminous flame
B. smoky flame
C. blue flame
D. green flame
Answer: B
Explanation: High carbon content produces sooty flame.
26. Terminal alkynes show acidic character due to
A. sp³ hybridisation
B. sp² hybridisation
C. sp hybridisation
D. resonance
Answer: C
Explanation: Higher s-character increases acidity.
27. Which reagent distinguishes terminal and non-terminal alkynes?
A. Bromine water
B. Baeyer’s reagent
C. Ammoniacal AgNO₃
D. HCl
Answer: C
Explanation: Terminal alkynes form silver acetylides.
Section E: Preparation of Hydrocarbons
28. Alkanes can be prepared by
A. Wurtz reaction
B. Kolbe’s reaction
C. decarboxylation
D. all of these
Answer: D
Explanation: Multiple methods exist for alkane preparation.
29. Alkenes are prepared by dehydration of
A. acids
B. alcohols
C. alkanes
D. alkynes
Answer: B
Explanation: Removal of water from alcohol gives alkene.
30. Alkynes can be prepared from
A. alkanes
B. alcohols
C. calcium carbide
D. aldehydes
Answer: C
Explanation: CaC₂ reacts with water to form ethyne.
Section F: Chemical Properties
31. Combustion of hydrocarbons produces
A. CO and H₂O
B. CO₂ and H₂O
C. CO₂ only
D. H₂ only
Answer: B
Explanation: Complete combustion forms CO₂ and water.
32. Incomplete combustion of hydrocarbons forms
A. CO₂
B. CO
C. carbon only
D. nitrogen
Answer: B
Explanation: Insufficient oxygen forms carbon monoxide.
33. Ozonolysis is a reaction of
A. alkanes
B. alkenes
C. alkynes
D. aromatics
Answer: B
Explanation: Ozone cleaves C=C bond.
34. Baeyer’s test is used to detect
A. alkanes
B. alkenes and alkynes
C. aromatics
D. alcohols
Answer: B
Explanation: KMnO₄ reacts with unsaturation.
Section G: Conceptual NCERT-Based MCQs
35. Which hydrocarbon is most reactive?
A. Alkane
B. Alkene
C. Alkyne
D. All are equal
Answer: C
Explanation: Alkynes have highest unsaturation.
36. Boiling point of alkanes increases with
A. branching
B. decrease in molecular mass
C. increase in molecular mass
D. unsaturation
Answer: C
Explanation: Larger molecules have stronger van der Waals forces.
37. Branched alkanes have
A. higher boiling point
B. lower boiling point
C. same boiling point
D. no boiling point
Answer: B
Explanation: Branching reduces surface area.
38. Which hydrocarbon shows cis-trans isomerism?
A. Ethane
B. Propane
C. But-2-ene
D. Ethyne
Answer: C
Explanation: Restricted rotation in double bond.
39. Which hydrocarbon is aromatic?
A. Ethene
B. Ethyne
C. Benzene
D. Propane
Answer: C
Explanation: Benzene is aromatic due to delocalised π electrons.
Section H: Application-Based MCQs
40. LPG mainly contains
A. methane
B. ethane
C. propane and butane
D. ethyne
Answer: C
Explanation: LPG is a mixture of propane and butane.
41. CNG is mainly
A. ethene
B. ethyne
C. methane
D. propane
Answer: C
Explanation: Compressed Natural Gas is rich in methane.
42. Which hydrocarbon is used for welding?
A. Methane
B. Ethane
C. Ethyne
D. Propene
Answer: C
Explanation: Oxy-acetylene flame has very high temperature.
Section I: High-Order Conceptual MCQs
43. Order of acidity is
A. alkane < alkene < alkyne
B. alkene < alkane < alkyne
C. alkyne < alkene < alkane
D. alkane = alkene = alkyne
Answer: A
Explanation: sp-hybridised carbon stabilises negative charge best.
44. Hyperconjugation stabilises
A. alkanes
B. alkenes
C. alkynes
D. aromatics only
Answer: B
Explanation: Alkene stability increases with alkyl substitution.
45. Which hydrocarbon gives maximum heat on combustion?
A. Alkane
B. Alkene
C. Alkyne
D. Aromatic
Answer: C
Explanation: Alkynes have highest carbon content.
Section J: Final Conceptual MCQs
46. Hydrocarbons are generally
A. ionic
B. polar
C. non-polar
D. metallic
Answer: C
Explanation: C–H bond is nearly non-polar.
47. Which hydrocarbon undergoes substitution most easily?
A. Alkane
B. Alkene
C. Alkyne
D. Benzene
Answer: A
Explanation: Alkanes undergo substitution reactions.
48. Which hydrocarbon is least reactive?
A. Alkane
B. Alkene
C. Alkyne
D. Benzene
Answer: A
Explanation: Alkanes are saturated and stable.
49. Which hydrocarbon does not decolourise bromine water?
A. Ethene
B. Ethyne
C. Benzene
D. Propene
Answer: C
Explanation: Benzene resists addition due to aromatic stability.
50. Hydrocarbons are important because they are
A. fuels and raw materials
B. acids
C. bases
D. catalysts
Answer: A
Explanation: Hydrocarbons are major energy sources and petrochemical feedstock.
✅ Completion Note
This completes a fully NCERT-aligned, CBSE-standard set of 50 MCQs on Hydrocarbons (Alkanes, Alkenes, Alkynes), ideal for concept clarity, revision, and board exam preparation.