Free practice › Class 11 › Chemistry › Chapter 9
Hydrocarbons — NEET & JEE MCQs with answers
Unit 9 covers the three major classes of hydrocarbons — alkanes (saturated, $\text{C}n\text{H}{2n+2}$), alkenes (one or more C=C double bond, $\text{C}n\text{H}{2n}$), and alkynes (one or more C≡C triple bond, $\text{C}n\text{H}{2n-2}$) — together with aromatic hydrocarbons (benzene and its derivatives). Each class is treated for structure, nomenclature, isomerism, preparation, and chemical properties, culminating in aromaticity (Hückel rule) and the carcinogenicity of polycyclic aromatic hydrocarbons.
Topics in this chapter
- 9.1 Classification of Hydrocarbons
- 9.2 Alkanes
- 9.3 Alkenes
- 9.4 Alkynes
- 9.5 Aromatic Hydrocarbons
- 9.6 Carcinogenicity and Toxicity of Hydrocarbons
Free practice questions
Monochlorination of methane (CH4 + Cl2, hv) gives as the first product
- A. Trichloromethane (CHCl3)
- B. Tetrachloromethane (CCl4)
- C. Dichloromethane (CH2Cl2)
- D. Chloromethane (CH3Cl)
Show answer
Answer: D — CH4 + Cl2 in light gives chloromethane (CH3Cl) + HCl, reaction 9.10.
NCERT Class 11 Chemistry · Ch 9 · 9.2 Alkanes
When bromine or chlorine adds to an alkene, the product formed is a
- A. trihalide
- B. geminal dihalide
- C. vicinal dihalide
- D. monohalide
Show answer
Answer: C — Halogens like bromine or chlorine add to an alkene to form vicinal dihalides (halogens on adjacent carbons).
NCERT Class 11 Chemistry · Ch 9 · 9.3.5 Properties
NCERT constructs all the alkyne structures possible for the molecular formula C5H8. How many structures are obtained?
- A. Two
- B. Three
- C. Five
- D. Seven
Show answer
Answer: B — NCERT (p.314) gives three structures for C5H8: pent-1-yne, pent-2-yne and 3-methylbut-1-yne (I and II are position isomers; I and III, or II and III, are chain isomers). Two is the number for butyne (C4H6), five is the number of alkene isomers of C5H10 (Problem 9.9), and seven is the number of C6H10 alkyne isomers in Problem 9.13.
NCERT Class 11 Chemistry · Ch 9 · 9.4 Alkynes
The carbocation intermediate formed when an electrophile attacks the benzene ring is called the:
- A. Arenium ion (sigma complex)
- B. Nitronium ion
- C. Carbanion
- D. Free radical
Show answer
Answer: A — Attack of the electrophile gives a sigma complex or arenium ion in which one carbon is sp3 hybridised.
NCERT Class 11 Chemistry · Ch 9 · 9.5 Aromatic Hydrocarbons
A hydrocarbon following the general formula CnH2n-2 belongs to the family of:
- A. Alkenes
- B. Cycloalkanes
- C. Alkanes
- D. Alkynes
Show answer
Answer: D — The general formula CnH2n-2 corresponds to alkynes, which contain a carbon-carbon triple bond.
NCERT Class 11 Chemistry · Ch 9 · 9.1 Classification of Hydrocarbons
The property of a substance to produce cancer is called:
- A. Carcinogenicity
- B. Basicity
- C. Aromaticity
- D. Volatility
Show answer
Answer: A — The cancer producing property of benzene and polynuclear hydrocarbons is referred to as carcinogenic (carcinogenicity).
NCERT Class 11 Chemistry · Ch 9 · 9.6 Carcinogenicity and Toxicity of Hydrocarbons
Alkynes on partial reduction with calculated dihydrogen over Lindlar's catalyst give
- A. a mixture giving only alkanes
- B. cis alkenes
- C. trans alkenes
- D. alkanes
Show answer
Answer: B — Partial reduction of alkynes with H2 over Lindlar's catalyst (palladised charcoal deactivated with sulphur compounds or quinoline) gives cis alkenes.
NCERT Class 11 Chemistry · Ch 9 · 9.3.4 Preparation
The standard enthalpy of combustion of methane (ΔcH) given in the text is approximately
- A. -397 kJ mol⁻¹
- B. -890 kJ mol⁻¹
- C. -12.5 kJ mol⁻¹
- D. -2875.84 kJ mol⁻¹
Show answer
Answer: B — For CH4(g) + 2O2(g) -> CO2(g) + 2H2O(l), ΔcH = -890 kJ mol^-1 (reaction 9.17).
NCERT Class 11 Chemistry · Ch 9 · 9.2 Alkanes
In benzene, the remaining sp2 hybrid orbital of each carbon overlaps with the s orbital of hydrogen to form:
- A. Six C–H sigma bonds
- B. Three C–C sigma bonds
- C. Three C–H pi bonds
- D. Six C–H pi bonds
Show answer
Answer: A — The remaining sp2 hybrid orbital of each carbon overlaps with the s orbital of a hydrogen atom to form six C–H sigma bonds.
NCERT Class 11 Chemistry · Ch 9 · 9.5 Aromatic Hydrocarbons
Which of the following is an unsaturated hydrocarbon?
- A. Cycloalkane
- B. Saturated open chain hydrocarbon
- C. Alkene
- D. Alkane
Show answer
Answer: C — Alkenes are unsaturated hydrocarbons because they contain carbon-carbon multiple (double) bonds, whereas alkanes and cycloalkanes are saturated.
NCERT Class 11 Chemistry · Ch 9 · 9.1 Classification of Hydrocarbons
Practise all 509 questions of Hydrocarbons in timed NEET & JEE tests
+4/−1 marking like the real exam · see which topics cost you marks · notes, XP and leaderboards
Start your free trial →