Questions about Aromatic Hydrocarbons (Organic Chemistry)
20 multiple-choice questions about Aromatic Hydrocarbons in Organic Chemistry, each with five alternatives (A–E). The answers with detailed explanations follow at the end.
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Multiple Choice Questions: Aromatic Hydrocarbons
1. What defines an aromatic hydrocarbon?
A) Contains only aliphatic chains
B) Contains nitrogen atoms
C) Contains a benzene ring or similar delocalized π system
D) Contains only triple bonds
E) Is insoluble in water
2. Which of the following compounds is aromatic?
A) Cyclopentane
B) Benzene
C) Ethene
D) Butyne
E) Propane
3. What is the molecular formula of benzene?
A) C₆H₁₂
B) C₆H₆
C) C₆H₁₀
D) C₅H₁₀
E) C₆H₈
4. What type of hybridization do carbon atoms in benzene have?
A) sp
B) sp²
C) sp³
D) dsp³
E) None
5. What does the term "delocalized electrons" refer to in benzene?
A) Electrons that are lost from the molecule
B) Electrons found in outer shells only
C) π electrons spread evenly over the ring
D) Electrons that are ionized
E) Electrons in the nucleus
6. Which of the following is not an aromatic hydrocarbon?
A) Toluene
B) Naphthalene
C) Cyclohexane
D) Xylene
E) Benzene
7. What is the IUPAC name of methylbenzene?
A) Benzyl
B) Benzene
C) Toluene
D) Phenol
E) Styrene
8. Which compound has two fused benzene rings?
A) Toluene
B) Xylene
C) Naphthalene
D) Aniline
E) Phenol
9. Which of the following is a property of aromatic hydrocarbons?
A) React vigorously with bromine in the dark
B) Undergo electrophilic substitution reactions
C) Are saturated compounds
D) Do not burn
E) Have linear structures
10. What type of reaction does benzene typically undergo?
A) Addition
B) Elimination
C) Electrophilic substitution
D) Neutralization
E) Hydrolysis
11. What is the name of benzene with a hydroxyl group attached?
A) Toluene
B) Phenol
C) Aniline
D) Acetophenone
E) Benzyl alcohol
12. What causes the high stability of benzene?
A) Strong C–C single bonds
B) High electronegativity
C) Resonance and delocalized π electrons
D) Presence of methyl groups
E) Aromaticity of hydrogen
13. What is the product when benzene reacts with Cl₂ in the presence of FeCl₃?
A) Chlorobenzene
B) Benzyl chloride
C) Benzene dichloride
D) Chloroethane
E) Benzoyl chloride
14. Which of the following is the correct structure for benzene?
A) Six carbon atoms in a straight chain
B) Six carbon atoms with alternating single and double bonds in a ring
C) Six carbon atoms with triple bonds in a ring
D) Five carbon atoms with one methyl group
E) A branched alkane
15. Which compound is commonly used as a moth repellent and contains fused benzene rings?
A) Benzene
B) Toluene
C) Naphthalene
D) Phenol
E) Xylene
16. How many π electrons are in a benzene ring?
A) 4
B) 6
C) 8
D) 10
E) 12
17. Which of the following is an aromatic hydrocarbon with three fused benzene rings?
A) Phenanthrene
B) Toluene
C) Styrene
D) Benzaldehyde
E) Xylene
18. What is Huckel's rule for aromaticity?
A) Compounds must have sp³ hybridization
B) Compounds must have 4n electrons
C) Compounds must have 4n + 2 π electrons in a planar ring
D) Compounds must contain oxygen
E) Compounds must be unsaturated
19. What is the primary environmental concern with aromatic hydrocarbons?
A) They are biodegradable
B) They are used as fertilizers
C) They can be toxic and carcinogenic
D) They purify the air
E) They react with water to form acid
20. What is the effect of resonance on aromatic compounds?
A) Increases reactivity
B) Decreases stability
C) Increases melting point
D) Increases stability and lowers reactivity
E) Makes them ionic
- Questions about Alkenes and Alkynes (Organic Chemistry)
- Questions about Structural Isomers and Stereoisomers (Organic Chemistry)
- Questions about Cyclic Hydrocarbons (Organic Chemistry)
✅ Answer Key with Extended Explanations
1. C – Aromatic hydrocarbons have a benzene ring or delocalized π system.
2. B – Benzene (C₆H₆) is the classic example of an aromatic hydrocarbon.
3. B – Benzene has the molecular formula C₆H₆.
4. B – Carbon atoms in benzene are sp² hybridized, allowing for delocalization.
5. C – Delocalized π electrons are shared across the ring, stabilizing the structure.
6. C – Cyclohexane is a cyclic alkane, not aromatic.
7. C – Methylbenzene is known as toluene.
8. C – Naphthalene is made of two fused benzene rings.
9. B – Aromatic hydrocarbons undergo electrophilic substitution rather than addition.
10. C – Benzene typically undergoes electrophilic substitution due to resonance stability.
11. B – Benzene with an –OH group is phenol.
12. C – The resonance of π electrons gives benzene its high stability.
13. A – Chlorination of benzene with FeCl₃ gives chlorobenzene.
14. B – Benzene is a ring of 6 carbon atoms with alternating single and double bonds.
15. C – Naphthalene is a moth repellent and has two fused aromatic rings.
16. B – Benzene has 6 π electrons from its three double bonds.
17. A – Phenanthrene has three fused benzene rings.
18. C – Huckel’s rule: A compound is aromatic if it has 4n + 2 π electrons in a planar ring.
19. C – Aromatic hydrocarbons are toxic and potentially carcinogenic pollutants.
20. D – Resonance increases the stability of aromatic compounds and reduces reactivity.
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