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NEET Chemistry: Aromatic Hydrocarbons Practice Questions

15 free multiple-choice questions on Aromatic Hydrocarbons for NEET Chemistry, each with the correct answer and a step-by-step explanation. Attempt a question, then reveal the solution to check your reasoning.

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  1. Q1. The nature of the electrophile determines the type of reaction. Which electrophile is usually used for the nitration of benzene?

    • ABr⁺
    • BNO₂⁺
    • CCl⁺
    • DH₂O⁺
    Show answer & explanation

    Correct answer: B — NO₂⁺

    Nitration of benzene requires the electrophile NO₂⁺, which is generated from the reaction of nitric acid and sulfuric acid (nitrating mixture).

  2. Q2. In a cyclic conjugated system, the energy difference between the actual molecule and its hypothetical Kekulé structure (with alternating double bonds) is small. This small energy difference is attributed to:

    • AThe stabilization provided by resonance and electron delocalization
    • BThe requirement for σ bond formation
    • CThe presence of steric hindrance
    • DThe increased bond angle strain
    Show answer & explanation

    Correct answer: A — The stabilization provided by resonance and electron delocalization

    The small energy difference is the manifestation of resonance stabilization, where the actual structure is a resonance hybrid of all possible Kekulé forms.

  3. Q3. If a ring is substituted with a strongly deactivating group, the overall rate of electrophilic substitution on that ring will be:

    • ADecreased significantly
    • BUnchanged
    • CReversible
    • DIncreased significantly
    Show answer & explanation

    Correct answer: A — Decreased significantly

    Deactivating groups decrease the overall electron density of the ring, making it less nucleophilic and therefore significantly slowing down the rate of electrophilic substitution.

  4. Q4. The reaction of benzene with a Friedel-Crafts acid catalyst results in the substitution of hydrogen atoms on the ring by an alkyl group. This type of reaction is classified as:

    • AElimination reaction
    • BElectrophilic aromatic substitution
    • CNucleophilic substitution
    • DElectrophilic addition
    Show answer & explanation

    Correct answer: B — Electrophilic aromatic substitution

    Friedel-Crafts reactions are classic examples of Electrophilic Aromatic Substitution (EAS), where an electrophile attacks the benzene ring.

  5. Q5. The stability of aromatic compounds compared to their non-aromatic counterparts (like cyclic alkenes) is primarily due to the presence of:

    • ALocalized lone pairs
    • BLocalized σ bonds
    • CIncreased angle strain
    • DResonance energy
    Show answer & explanation

    Correct answer: D — Resonance energy

    Aromatic stability is derived from the extensive delocalization of π electrons, which leads to resonance stabilization energy, making the aromatic system significantly more stable than a hypothetical localized structure.

  6. Q6. Which of the following reagents is used to catalyze the Friedel-Crafts alkylation reaction?

    • AAlCl₃
    • BH₂SO₄
    • CH₂O
    • DHCl
    Show answer & explanation

    Correct answer: A — AlCl₃

    Aluminum chloride (AlCl₃) acts as a Lewis acid catalyst, complexing with the alkyl halide to generate the electrophile (R⁺) necessary for the reaction.

  7. Q7. In the Friedel-Crafts reaction, the reaction occurs at which part of the aromatic ring?

    • AThe σ bond connecting the ring carbons
    • BThe π electron system of the ring
    • CThe π bond of the ring
    • DThe σ bond of the ring
    Show answer & explanation

    Correct answer: B — The π electron system of the ring

    Electrophilic substitution reactions, like Friedel-Crafts, occur via the attack of the electrophile on the π electron system of the aromatic ring, breaking the aromaticity temporarily.

  8. Q8. In Friedel-Crafts acylation, which group is typically used to introduce an acyl group (RCO-) onto the benzene ring?

    • AAcyl chlorides or acid anhydrides
    • BPhenols
    • CAlkyl halides
    • DAlkenes
    Show answer & explanation

    Correct answer: A — Acyl chlorides or acid anhydrides

    Friedel-Crafts acylation involves reacting an aromatic compound with an acylating agent (like acyl chloride or anhydride) and a Lewis acid catalyst, leading to the introduction of the acyl group.

  9. Q9. Benzene is considered aromatic primarily because it exhibits significant delocalization of its pi electrons over the entire ring. This delocalization results in which characteristic property of the benzene molecule?

    • AHigh bond dissociation energy.
    • BPlanar geometry and ring strain.
    • CComplete free rotation of all bonds.
    • DA stable, cyclic, and highly stable structure with equal bond lengths.
    Show answer & explanation

    Correct answer: D — A stable, cyclic, and highly stable structure with equal bond lengths.

    The delocalization of pi electrons across the cyclic structure of benzene leads to a highly stable configuration. This extensive delocalization results in a planar geometry and highly symmetrical bond lengths, which contributes significantly to its aromatic stability.

  10. Q10. The product formed by Friedel-Crafts alkylation involves the addition of which group to the benzene ring?

    • A-NO₂
    • B-OH
    • C-COCl
    • DAlkyl group (R)
    Show answer & explanation

    Correct answer: D — Alkyl group (R)

    Friedel-Crafts alkylation specifically introduces an alkyl group (R) onto the benzene ring via electrophilic substitution.

  11. Q11. Which of the following compounds is typically the most reactive towards electrophilic substitution among the benzene derivatives?

    • AChlorobenzene
    • BBromobenzene
    • CBenzene
    • DNitrobenzene
    Show answer & explanation

    Correct answer: C — Benzene

    Benzene is the parent aromatic compound and serves as the baseline for electrophilic substitution.

  12. Q12. Which of the following statements correctly describes the extent of π-electron delocalization in the benzene ring?

    • ATen π electrons are delocalized, which is characteristic of an anti-aromatic system.
    • BSix π electrons are delocalized, resulting in a stable cyclic system.
    • CEight π electrons are delocalized, leading to aromatic stabilization.
    • DOnly two π electrons are delocalized across the ring.
    Show answer & explanation

    Correct answer: B — Six π electrons are delocalized, resulting in a stable cyclic system.

    Benzene possesses six π electrons (one from each C-H bond) that are delocalized over the entire cyclic structure, making it an aromatic system. This cyclic delocalization leads to significant stabilization (aromaticity).

  13. Q13. Which of the following compounds is generally most reactive towards electrophilic substitution?

    • ANitrobenzene
    • BChlorobenzene
    • CPhenol
    • DBenzene
    Show answer & explanation

    Correct answer: D — Benzene

    Benzene is the parent aromatic compound. While phenol is highly reactive, benzene serves as the baseline for simple electrophilic substitution reactions; it is the most readily substituted system among the basic forms.

  14. Q14. The reaction of benzene with CH₃Cl in the presence of AlCl₃ results in the formation of which product?

    • ABenzene C₆H₅CH₃
    • BChlorobenzene
    • CBenzene-1-methylbenzene
    • DToluene
    Show answer & explanation

    Correct answer: D — Toluene

    This is the Friedel-Crafts Alkylation. The electrophile (CH₃⁺) attacks the benzene ring, resulting in the addition of a methyl group, yielding Toluene.

  15. Q15. Which of the following is NOT a necessary condition for a compound to exhibit aromatic character?

    • AThe system must be cyclic.
    • BThe system must have an odd number of π electrons.
    • CThe system must have continuous π electron overlap.
    • DThe system must be planar.
    Show answer & explanation

    Correct answer: B — The system must have an odd number of π electrons.

    Aromaticity requires an even number of π electrons of the (4n+2) rule, not an odd number. The other three options describe the essential geometrical and electron system requirements.

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