MCQs on Haloalkanes and Haloarenes – Class 12 Chemistry
MCQs on Haloalkanes and Haloarenes – CBSE Class 12 Chemistry
Organic Chemistry | NCERT-Based | MCQs with Answers & Explanations
The following 50 Multiple Choice Questions (MCQs) are strictly prepared as per the NCERT syllabus for CBSE Class 12 Chemistry.
They are arranged section-wise to cover classification, nomenclature, methods of preparation, physical properties, chemical reactions (SN1, SN2, elimination), and uses of haloalkanes and haloarenes, with clear, concept-focused explanations suitable for board exam preparation.
Section A: Classification & Nomenclature
Q1. Haloalkanes are compounds in which halogen is attached to:
A. sp² carbon
B. sp carbon
C. sp³ carbon
D. Aromatic carbon
Answer: C
Explanation:
In haloalkanes, halogen is bonded to an sp³-hybridised carbon atom.
Q2. Haloarenes are compounds in which halogen is attached to:
A. Aliphatic carbon
B. sp³ carbon
C. Aromatic ring carbon
D. Carbonyl carbon
Answer: C
Explanation:
In haloarenes, the halogen atom is directly bonded to an aromatic (sp²) carbon.
Q3. Which of the following is a primary haloalkane?
A. (CH₃)₃CCl
B. CH₃CH₂Cl
C. CH₃CHClCH₃
D. C₆H₅CHClCH₃
Answer: B
Explanation:
In CH₃CH₂Cl, the halogen is attached to a primary carbon atom.
Q4. The IUPAC name of CH₃–CHCl–CH₃ is:
A. 1-Chloropropane
B. 2-Chloropropane
C. Isopropyl chloride
D. Propyl chloride
Answer: B
Explanation:
The chlorine atom is attached to the second carbon, hence 2-chloropropane.
Q5. Which compound is an aryl halide?
A. CH₃Cl
B. C₂H₅Br
C. C₆H₅Cl
D. CH₂Cl₂
Answer: C
Explanation:
Chlorobenzene (C₆H₅Cl) is an aryl halide (haloarene).
Section B: Nature of C–X Bond & Physical Properties
Q6. The C–X bond in haloalkanes is polar because:
A. Carbon is more electronegative than halogen
B. Halogen is more electronegative than carbon
C. Carbon is larger than halogen
D. Carbon has vacant orbitals
Answer: B
Explanation:
Halogens are more electronegative, making the C–X bond polar.
Q7. Which haloalkane has the highest boiling point?
A. CH₃Cl
B. CH₃Br
C. CH₃I
D. CH₄
Answer: C
Explanation:
Boiling point increases with molecular mass due to stronger van der Waals forces.
Q8. The solubility of haloalkanes in water is low because:
A. They are heavy
B. They cannot form hydrogen bonds with water
C. They are non-polar
D. They react with water
Answer: B
Explanation:
Haloalkanes cannot form strong hydrogen bonds with water molecules.
Q9. Which factor mainly affects the reactivity of haloalkanes in nucleophilic substitution?
A. Length of carbon chain
B. Strength of C–X bond
C. Color of compound
D. Density
Answer: B
Explanation:
Weaker C–X bond leads to higher reactivity.
Q10. Correct order of C–X bond strength is:
A. C–I > C–Br > C–Cl > C–F
B. C–F > C–Cl > C–Br > C–I
C. C–Cl > C–F > C–I > C–Br
D. C–Br > C–Cl > C–F > C–I
Answer: B
Explanation:
Bond strength decreases with increasing atomic size of halogen.
Section C: Methods of Preparation
Q11. Haloalkanes can be prepared from alcohols using:
A. NaOH
B. H₂SO₄
C. PCl₅
D. KMnO₄
Answer: C
Explanation:
PCl₅ converts alcohols into alkyl chlorides.
Q12. Which reagent is used to prepare alkyl bromides from alcohols?
A. PCl₅
B. SOCl₂
C. HBr
D. Cl₂
Answer: C
Explanation:
HBr replaces –OH group with Br atom.
Q13. Chlorobenzene cannot be prepared by direct reaction of:
A. Benzene + Cl₂/FeCl₃
B. Phenol + HCl
C. Sandmeyer reaction
D. Gattermann reaction
Answer: B
Explanation:
Phenol does not react with HCl to give chlorobenzene.
Q14. Which reaction converts alkene to vicinal dihalide?
A. Wurtz reaction
B. Finkelstein reaction
C. Addition of halogen
D. Swarts reaction
Answer: C
Explanation:
Halogens add across the double bond of alkenes.
Q15. Which reaction is used to prepare fluorides from chlorides or bromides?
A. Wurtz reaction
B. Swarts reaction
C. Sandmeyer reaction
D. Finkelstein reaction
Answer: B
Explanation:
Swarts reaction replaces Cl or Br by fluorine.
Section D: Chemical Reactions – Nucleophilic Substitution
Q16. SN1 reaction proceeds through formation of:
A. Free radical
B. Carbocation
C. Carbanion
D. Carbine
Answer: B
Explanation:
SN1 reaction involves a carbocation intermediate.
Q17. Which haloalkane undergoes SN1 reaction most easily?
A. CH₃Cl
B. C₂H₅Cl
C. (CH₃)₃CCl
D. CH₃CH₂CH₂Cl
Answer: C
Explanation:
Tertiary carbocation is most stable, favoring SN1.
Q18. SN2 reactions are favored by:
A. Tertiary haloalkanes
B. Secondary haloalkanes
C. Primary haloalkanes
D. Aryl halides
Answer: C
Explanation:
Less steric hindrance favors backside attack in SN2.
Q19. Which solvent favors SN1 reaction?
A. Hexane
B. Benzene
C. Water
D. Ether
Answer: C
Explanation:
Polar protic solvents stabilize carbocations and anions.
Q20. SN2 reaction leads to:
A. Retention of configuration
B. Racemisation
C. Inversion of configuration
D. No change
Answer: C
Explanation:
Backside attack causes Walden inversion.
Section E: Elimination & Other Reactions
Q21. Dehydrohalogenation of haloalkanes gives:
A. Alcohol
B. Alkene
C. Alkane
D. Ether
Answer: B
Explanation:
Elimination of HX leads to alkene formation.
Q22. Which base is commonly used in dehydrohalogenation?
A. Aqueous KOH
B. Alcoholic KOH
C. NaCl
D. HCl
Answer: B
Explanation:
Alcoholic KOH favors elimination reactions.
Q23. The major product of dehydrohalogenation follows:
A. Markovnikov’s rule
B. Saytzeff’s rule
C. Anti-Markovnikov rule
D. Huckel’s rule
Answer: B
Explanation:
More substituted alkene is formed as the major product.
Q24. Wurtz reaction is used to prepare:
A. Alkenes
B. Alcohols
C. Alkanes
D. Alkynes
Answer: C
Explanation:
Two alkyl halides couple to form alkanes.
Q25. Which reagent converts haloalkane into alcohol?
A. Alcoholic KOH
B. Aqueous KOH
C. Na metal
D. Mg in ether
Answer: B
Explanation:
Aqueous KOH causes nucleophilic substitution to form alcohol.
Section F: Haloarenes – Properties & Reactions
Q26. Haloarenes are less reactive towards nucleophilic substitution because:
A. C–X bond is weaker
B. Presence of partial double bond character
C. Steric hindrance
D. High polarity
Answer: B
Explanation:
Resonance gives the C–X bond partial double bond character, strengthening it.
Q27. Which haloarene is most reactive towards nucleophilic substitution?
A. Chlorobenzene
B. Bromobenzene
C. Iodobenzene
D. Fluorobenzene
Answer: D
Explanation:
Strong −I effect of F stabilizes the transition state.
Q28. Chlorobenzene undergoes substitution only under drastic conditions because:
A. C–Cl bond is weak
B. Carbon is sp³ hybridised
C. C–Cl bond is strong due to resonance
D. Chlorine is bulky
Answer: C
Explanation:
Resonance increases bond strength in haloarenes.
Q29. Which reaction converts chlorobenzene into phenol?
A. Finkelstein reaction
B. Dow’s process
C. Wurtz reaction
D. Swarts reaction
Answer: B
Explanation:
Dow’s process uses NaOH at high temperature and pressure.
Q30. Haloarenes undergo electrophilic substitution mainly at:
A. Meta position
B. Ortho and para positions
C. Side chain
D. Any position
Answer: B
Explanation:
Halogens are ortho-para directing due to resonance.
Section G: Environmental & Applied Aspects
Q31. Which compound is used as an anesthetic?
A. CHCl₃
B. CCl₄
C. CH₂Cl₂
D. C₂H₅Cl
Answer: A
Explanation:
Chloroform was historically used as an anesthetic.
Q32. Which compound is responsible for ozone layer depletion?
A. CH₃Cl
B. CHCl₃
C. CCl₄
D. Freons
Answer: D
Explanation:
Freons release chlorine radicals that destroy ozone.
Q33. DDT is an example of:
A. Alkyl halide
B. Aryl halide
C. Mixed halide
D. Polyhalogen compound
Answer: D
Explanation:
DDT contains multiple halogen atoms.
Q34. Which haloalkane reacts fastest with AgNO₃ in ethanol?
A. CH₃Cl
B. C₂H₅Cl
C. (CH₃)₃CCl
D. CH₃CH₂CH₂Cl
Answer: C
Explanation:
AgNO₃ in ethanol favors SN1 reaction, fastest for tertiary halides.
Q35. Which compound gives precipitate fastest with alcoholic AgNO₃?
A. R–Cl
B. R–Br
C. R–I
D. R–F
Answer: C
Explanation:
C–I bond is weakest, so iodides react fastest.
Section H: NCERT-Based Mixed MCQs
Q36. Which compound shows optical isomerism?
A. CH₃CH₂Cl
B. CH₃CHClCH₃
C. CH₃CHClCOOH
D. CCl₄
Answer: C
Explanation:
Presence of chiral carbon causes optical activity.
Q37. Which reagent converts alkyl halide into nitrile?
A. KCN
B. AgCN
C. NaOH
D. NH₃
Answer: A
Explanation:
KCN gives alkyl cyanides via SN2.
Q38. Which reaction increases carbon chain length by one carbon?
A. Wurtz reaction
B. Reaction with KCN
C. Dehydrohalogenation
D. Hydrolysis
Answer: B
Explanation:
CN group adds one extra carbon.
Q39. Which compound does not undergo SN1 reaction?
A. Tert-butyl chloride
B. Benzyl chloride
C. Allyl chloride
D. Chlorobenzene
Answer: D
Explanation:
Chlorobenzene does not form stable carbocation.
Q40. Which haloalkane undergoes fastest SN2 reaction?
A. CH₃Cl
B. CH₃Br
C. CH₃I
D. C₂H₅Cl
Answer: C
Explanation:
Weakest C–X bond and least steric hindrance.
Q41. Which compound forms Grignard reagent most easily?
A. R–Cl
B. R–Br
C. R–I
D. Ar–Cl
Answer: C
Explanation:
Iodides react fastest with magnesium.
Q42. Haloarenes do not undergo SN2 reaction because:
A. Steric hindrance
B. sp² carbon does not allow backside attack
C. High electronegativity
D. Low polarity
Answer: B
Explanation:
Backside attack is not possible on sp² carbon.
Q43. Which solvent favors SN2 reaction?
A. Water
B. Alcohol
C. Acetone
D. Formic acid
Answer: C
Explanation:
Polar aprotic solvents favor SN2 mechanism.
Q44. Which is least reactive in nucleophilic substitution?
A. Allyl chloride
B. Benzyl chloride
C. Chlorobenzene
D. Ethyl chloride
Answer: C
Explanation:
Resonance-stabilized C–Cl bond resists substitution.
Q45. Which reaction is used to couple two alkyl halides?
A. Swarts reaction
B. Wurtz reaction
C. Sandmeyer reaction
D. Finkelstein reaction
Answer: B
Explanation:
Wurtz reaction couples alkyl halides using sodium.
Q46. The major product when 2-bromopropane reacts with alcoholic KOH is:
A. Propane
B. Propene
C. 1-Propanol
D. 2-Propanol
Answer: B
Explanation:
Elimination leads to propene.
Q47. Which compound is used as a refrigerant?
A. CHCl₃
B. CCl₄
C. Freon-12
D. CH₃Cl
Answer: C
Explanation:
Freon-12 was widely used as a refrigerant.
Q48. Which halogen shows strongest −I effect?
A. I
B. Br
C. Cl
D. F
Answer: D
Explanation:
Fluorine has highest electronegativity.
Q49. Which compound undergoes fastest elimination?
A. Primary halide
B. Secondary halide
C. Tertiary halide
D. Methyl halide
Answer: C
Explanation:
Tertiary halides form stable carbocations, favoring elimination.
Q50. Haloalkanes are generally prepared from alcohols by replacing:
A. Hydrogen
B. Oxygen
C. –OH group
D. Carbon
Answer: C
Explanation:
The –OH group of alcohol is replaced by halogen.
✅ CBSE Exam Tip:
These MCQs are fully NCERT-aligned, concept-focused, and ideal for Class 12 board exams, revision, and objective practice.