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This article provides important MCQs for CBSE Class 12 Chemistry Chapter – Haloalkanes and Haloarenes. The questions and answers are available in PDF format and are based on the revised CBSE syllabus. These questions are crafted by experienced teachers, making them one of the best resources for exam preparation. Practicing these MCQs will help strengthen your concepts and improve weak areas.
Haloalkanes and Haloarenes are derivatives of hydrocarbons with one or more halogen groups (like iodine, bromine, chlorine, etc.) replacing hydrogen atoms. The main difference between them is that haloalkanes are derived from open-chain alkanes, while haloarenes come from aromatic hydrocarbons with a ring structure.
These compounds are classified based on the number of hydrogen atoms and the type of carbon-halogen bond (sp3 C-X bond and sp2 C-X bond, where X represents the halogen group). Haloalkanes and haloarenes have various commercial uses, such as in fire extinguishers and solvents.
Class 12 Chemistry MCQ Haloalkanes and Haloarenes
Ques 1. Which sequence should isomeric dichlorobenzenes be boiled in?
a) para>ortho>meta
b) meta>ortho>para
c) ortho>meta>para
d) para>meta>ortho
Answer: a
Explanation: In comparison to meta and ortho isomers, para isomers have the highest melting temperatures due to their symmetry and ease of fitting into a crystal lattice.
Ques 2. Which of the following substances has the highest melting point?
a) Chloromethane
b) Tetrachloromethane
c) Trichloromethane
d) Dichloromethane
Answer: b
Explanation: As the molecule masses and the number of halogen atoms grows, the boiling points and intermolecular forces of attraction increase as well.
Ques 3. Which of the following is the right name for the compound H₃C-CHCl₂?
a) 1,2-Dichloroethane
b) Ethylene dichloride
c) Ethylidene chloride
d) Vic-dichloride
Answer: c
Explanation: Both halogens are on the same carbon atom in the given molecule, making it a dihaloalkane. These are also known as alkylidene halides or gem-dihalides.
Ques 4. Which of the following statements about the interaction between C₂H₄ and Cl₂ in CCl₄ is incorrect?
a) It results in the formation of a vicinal dihalide
b) It results in the discharge of a reddish-brown colour
c) It results in the formation of a colourless compound
d) It results in the breaking of the C-C double bond
Answer: b
Explanation: When Br₂ interacts with an alkene to generate a vic-dihalide, it gives off a reddish-brown colour. As a result, it’s a crucial test for detecting a double bond.
Also Check: Haloalkanes and Haloarenes Class 12 Notes Chemistry Chapter 10
Ques 5. Which of the following statements about SN2 mechanisms is incorrect?
a) The transition state is stable
b) The complete mechanism takes place in a single step
c) The rate of the reaction depends on the concentration of both reactants
d) There is an inversion of configuration
Answer: a
Explanation: The carbon atoms are concurrently attached to the entering nucleophile and the existing group in the transition state of SN2 processes, and are thus connected to five atoms at the same time. It is impossible to isolate such a geometry since it is unstable.
Ques 6. Which of the following is a primary halide?
a) Isopropyl iodide
b) Secondary butyl iodide
c) Tertiary butyl iodide
d) Neohexyl chloride
Answer: d
Ques 7. Which among the given substances possesses the maximum dipole moment?
a) CH₃Br
b) CH₃Cl
c) CH₃F
d) None of the above
Answer: b
Explanation: The halogen groups possess high electronegativity and exhibit intense dipole moments. In comparison with bromine and chlorine, fluorine has the maximum electronegativity. The dipole moment of CH₃F is restricted by the smaller distance between the carbon and fluorine groups. Therefore, CH₃Cl poses the highest dipole moment.
Ques 8. Which of the following is most reactive towards nucleophilic substitution reaction?
a) C₆H₅Cl
b) CH₂=CHCl
c) ClCH₂CH=CH₂
d) CH₃CH=CHCl
Answer: c
Ques 9. The most reactive nucleophile among the following is
a) CH₃O⁻
b) C₆H₅O⁻
c) (CH₃)₂CHO⁻
d) (CH₃)₃CO⁻
Answer: a
Ques 10. The main difference between C-X bond of a haloalkane and a haloarene is
a) C-X bond in haloalkanes is shorter than haloarenes
b) In haloalkanes the C attached to halogen in C-X bond is sp³ hybridised while in haloarenes it is sp² hybridised.
c) C-X bond in haloalkanes acquires a double bond character due to higher electronegativity of X than haloarenes.
d) Haloalkanes are less reactive than haloarenes due to difficulty in C-X cleavage in haloalkanes.
Answer: b
Also Check: NCERT Exemplar Solutions for Class 12 Chemistry Chapter 10 – Haloalkanes and Haloarenes
Ques 11. Which among the following is the halogenation of alkanes?
a) An isothermal process
b) An endothermic process
c) A reductive process
d) An oxidative process
Answer: d
Explanation: Halogenation of alkanes is an oxidative process since ultraviolet light or heat (energy sources to promote homolytic cleavage of halogen groups) are used to collide with alkane, resulting in haloalkanes or alkyl halides.
Ques 12. What is 3-Bromopropene’s common name?
a) Allyl bromide
b) Vinyl bromide
c) Tert-Butyl bromide
d) Propylidene bromide
Answer: a
Explanation: The parent chain of 3-Bromopropene has three C atoms, with a double bond at C-1 and Br at C-3. As a result, it is an allylic halide because Br is connected to the C adjacent to the C-C double bond.
Ques 13. What is the catalyst in the chloroalkane reaction of a primary alcohol with HCl?
a) Red phosphorous
b) Concentrated H₂SO₄
c) Anhydrous ZnCl₂
d) Pyridine
Answer: c
Explanation: The presence of anhydrous ZnCl₂ in alcohols is supposed to disrupt the C-O bond. ZnCl₂ is a Lewis acid that reacts with the alcohol group’s oxygen.
Ques 14. When ethanol combines with PCl₅, it produces three products: chloroethane, hydrochloric acid, and ______. What is the third item on the list?
a) Phosphorus acid
b) Phosphoryl chloride
c) Phosphorus trichloride
d) Phosphoric acid
Answer: b
Explanation: CH₃CH₂OH reacts with PCl₅ to produce CH₃CH₂Cl, POCl₃ (phosphoryl acid), and HCl. This is a procedure for making chloroalkanes from alcohols.
Ques 15. Which of the following haloalkanes is optically active?
a) 1-Chloropropane
b) 1-Bromopropane
c) 1-Iodopropane
d) 1-Fluoropropane
Answer: b
Ques 16. Aryl halides are less reactive towards nucleophilic substitution reactions as compared to alkyl halides due to
a) Formation of a less stable carbonium ion in aryl halides
b) Resonance stabilization in aryl halides
c) Presence of double bonds in alkyl halides
d) Inductive effect in aryl halides
Answer: b
Ques 17. p-dichlorobenzene has higher melting point than its o- and m- isomers. Why?
a) m-dichlorobenzene is more polar than o-isomer
b) p-isomer has a symmetrical crystalline structure
c) Boiling point of o- isomer is more than p-isomers
d) All of these are correct
Answer: b
Ques 18. Chlorobenzene on reaction with NaOH at 300K followed by acidic hydrolysis produces
a) Phenol
b) Sodium phenoxide
c) Benzaldehyde
d) Benzoic acid
Answer: a
Ques 19. Which of the following is most reactive towards aqueous NaOH?
a) C₆H₅Cl
b) C₆H₅CH₂Cl
c) C₆H₅Br
d) BrC₆H₄Br
Answer: b
Ques 20. The SN1 reaction in alkyl halides results in
a) Retention of configuration
b) Partial racemization
c) Inversion of configuration
d) All of the above
Answer: b
Explanation: Racemization is a conversion process associated with the SN1 reaction of alkyl halides. It is so because the SN1 reaction of optically active alkyl halide exhibits nucleophilic attack from two sides to form bonds with the trigonal planar structure. Therefore, this reaction results in partial racemization conversion.
Ques 21. Which of the following is the class of the substitution product of LiAlH₄ and an alkyl halide reaction?
a) Haloalkane
b) Alkyl nitrite
c) Nitroalkane
d) Hydrocarbon
Answer: d
Explanation: The H atom in LiAlH₄ acts as a nucleophile, attacking and substituting the halogen in the alkyl halide to generate the basic hydrocarbon.
Ques 22. A mono haloarene is an example of __________
a) Aliphatic halogen compound
b) Side-chain substituted aryl halide
c) Alkyl halide
d) Aromatic halogen compound
Answer: d
Explanation: A mono haloarene is a halogenated benzene ring with the halogen linked straight to it. Aromatic halogen compounds with the halogen not directly linked to the benzene ring are side chain substituted aryl halides.
Ques 23. Among the given arrangement of halogen groups, identify the appropriate order of the halogens based on the increasing order of nucleophilicity?
a) Cl⁻ <Br⁻ < I⁻
b) F⁻ < Br⁻ < Cl⁻
c) Cl⁻ < Br⁻ < F⁻
d) Br⁻ < Cl⁻ < I⁻
Answer: a
Explanation: The elements placed in the downward direction of the periodic table tend to possess larger atomic sizes. In such groups, the electrons are not closely bound to the nucleus, so they can easily lose them to form new C-X bonds. Therefore, the nucleophilicity increases from Cl⁻ < Br⁻ < I⁻.
Ques 24. Chloropicrin is a product synthesized by the reaction between
a) Steam over carbon tetrachloride
b) Chlorine over picric acid
c) Nitric acid over chlorobenzene
d) Nitric acid over chloroform
Answer: d
Explanation: Chloropicrin is a product obtained through the reaction between nitric acid and chloroform. In this reaction step, upon treating the chloroform with concentrated nitric acid, the hydrogen group present in the chloroform is replaced by the nitro group from the nitric acid giving rise to the product as mentioned earlier.
Ques 25. Among the following, which alkyl halides have the strongest C – X bond?
a) CH₃Br
b) CH₃Cl
c) CH₃I
d) CH₃F
Answer: d
Explanation: Since the halogen atom is highly electronegative in comparison to the carbon atom, the electrostatic bond between fluorine and carbon is so strong that it pulls the electron pair towards itself instead of the carbon atom. Therefore, the C-F bond possesses the highest bond strength.
Ques 26. Phosgene is a common name for a gaseous chemical called
a) Carbonyl chloride
b) Thionyl chloride
c) Carbon dioxide with phosphine
d) None of the above
Answer: a
Explanation: Carbonyl chloride or COCl₂ is also identified as phosgene as its common name. It is a transparent, unpleasant odor carrying poisonous gas known to exhibit severe irritation to the eyes, throat, and rest of the respiratory system upon exposure. It has a broad spectrum of applications in the plastic and pesticide industries.
Ques 27. The commercial preparation of a chemical substance called chlorobenzene is carried out using the following processes?
a) Grignard reaction
b) Friedel-Crafts reaction
c) Wurtz Fittig reaction
d) Raschig process
Answer: d
Explanation: The Raschig-Hooker is a chemical process used by industries to produce phenols. It is also used for the commercial preparation of chlorobenzene. A copper oxide catalyst is used in this process to treat benzene vapours in the presence of hydrogen chloride gas and oxygen at a temperature of 250 degrees Celsius.
Ques 28. _______ possesses the highest melting point among the given set of compounds?
a) o-Dichlorobenzene
b) p-Dichlorobenzene
c) m-Dichlorobenzene
d) All of the Given
Answer: b
Explanation: A para isomer of a given chemical molecule has higher symmetry, which allows the molecule to remain within a crystal better than an ortho or meta isomer. Therefore, the p-dichlorobenzene or the para isomers possess a higher melting point and low solubility than their ortho (o) or meta (m) counterparts.
Ques 29. Ethylene dichloride is prepared by the addition of hydrochloric acid to _________
a) Methane
b) Ethylene
c) Propane
d) Ethylene glycol
Answer: d
Explanation: The ethylene dichloride is synthesized by the addition of hydrochloric acid to ethylene glycol. In this reaction step, the CH₂OH⋅CH₂OH (ethylene glycol), when mixed with 2HCl (hydrochloric acid), produces C₂H₄Cl₂ (ethylene dichloride) and 2H₂O (water). The chlorine group replaces the hydroxyl group in ethylene glycol, an example of a displacement reaction.
