NEET-Level Practice: Haloalkanes and Haloarenes

A focused NEET-UG practice quiz on Haloalkanes and Haloarenes — classification and nomenclature, named reactions (Finkelstein, Swarts, Sandmeyer, Wurtz), the SN1/SN2 distinction and reactivity, optical isomerism and chirality, Saytzeff's rule, the low reactivity of haloarenes, and the uses and environmental effects of polyhalogen compounds. Identify the substrate type first. Each question has a concise explanation.

--- QUIZ (Hard) --- Section 13 Quiz: NEET Previous Year Questions

Q1. R-Cl + NaI in dry acetone -> R-I is the: A) Swarts reaction *B) Finkelstein reaction C) Wurtz reaction D) Sandmeyer reaction Explanation: Finkelstein reaction converts alkyl chlorides/bromides to alkyl iodides using NaI in dry acetone.

Q2. Inversion of configuration occurs in: A) SN1 *B) SN2 C) E1 D) Free radical Explanation: SN2 proceeds by backside attack, giving Walden inversion.

Q3. Which depletes the ozone layer? A) DDT *B) Freon (CFC) C) Iodoform D) Ethanol Explanation: Chlorofluorocarbons (CFCs), such as freons, are ozone-depleting substances.

Q4. The Swarts reaction prepares alkyl: A) iodides *B) fluorides C) chlorides D) bromides Explanation: In Swarts reaction, alkyl chlorides or bromides are converted to alkyl fluorides using metal fluorides such as AgF, Hg2_2F2_2, or SbF3_3.

Q5. A chiral carbon is bonded to: A) Two different groups *B) Four different groups C) Four identical groups D) Three groups Explanation: A tetrahedral carbon attached to four different groups is chiral.

Q6. SN1 reactivity is highest for: A) Methyl halide A) Primary halide *C) Tertiary halide D) Vinyl halide Explanation: Tertiary halides form the most stable carbocations, so they react fastest by SN1.

Q7. Alcoholic KOH converts an alkyl halide to a/an: A) Alcohol *B) Alkene C) Alkane D) Ether Explanation: Alcoholic KOH favours β-elimination (dehydrohalogenation), producing an alkene.

Q8. The major product in elimination follows … rule: A) Markovnikov *B) Saytzeff C) Hund D) Aufbau Explanation: Saytzeff's rule: the more substituted alkene is generally the major product.

Q9. A racemic mixture is: A) Optically active *B) Optically inactive (rotations cancel) C) A single enantiomer D) Achiral always Explanation: A racemic mixture contains equal amounts of two enantiomers, so the optical rotations cancel.

Q10. The Wurtz reaction uses: A) Mg/dry ether *B) Na/dry ether C) NaI/acetone D) CuCl/HCl Explanation: Wurtz reaction couples alkyl halides using sodium metal in dry ether.

Q11. Chlorobenzene is … reactive than chloroethane toward nucleophiles: A) More *B) Less C) Equally D) Infinitely more Explanation: In chlorobenzene, the C-Cl bond has partial double-bond character due to resonance and the carbon is sp2^2-hybridised, so nucleophilic substitution is much more difficult than in chloroethane.

Q12. In a haloarene, the halogen is: A) Activating, meta-directing *B) Deactivating, ortho/para-directing C) Activating, ortho/para-directing D) Deactivating, meta-directing Explanation: Halogens withdraw by -I effect, so they are deactivating; but their lone pairs donate by resonance, making them ortho/para-directing.

Q13. Iodoform's antiseptic action is due to: A) The CHI3_3 molecule *B) Free iodine C) Carbon D) Iodide ion Explanation: Iodoform slowly liberates free iodine, which is responsible for its antiseptic action.

Q14. The best leaving group is: A) F- B) Cl- C) Br- *D) I- Explanation: Iodide is the best leaving group among halides because HI is the strongest acid and I- is the most stable/polarisable.

Q15. Vinyl chloride (CH2_2=CHCl) has the C-Cl carbon as: A) sp3^3 *B) sp2^2 C) sp D) ionic Explanation: The carbon bonded to Cl is part of the double bond, so it is sp2^2-hybridised.

Q16. DDT is: A) Biodegradable *B) Non-biodegradable and bioaccumulating C) Water-soluble D) A refrigerant Explanation: DDT is persistent in the environment and accumulates in food chains.

Q17. The Sandmeyer reaction converts a diazonium salt to: A) An alcohol *B) An aryl halide C) An alkene D) An amine Explanation: Aryl diazonium salts react with cuprous salts (CuCl, CuBr, CuCN) to form substituted aryl compounds, including aryl halides.

Q18. Chloroform on standing in air and light forms: A) CO2_2 *B) Phosgene (COCl2_2) C) CO D) Cl2_2 Explanation: Chloroform undergoes oxidation in air and light to form poisonous phosgene (COCl2_2).

Q19. (CH3_3)3_3CCl is classified as: A) Primary B) Secondary *C) Tertiary D) Aryl Explanation: The carbon attached to Cl is bonded to three carbon atoms, so it is tertiary.

Q20. CH2_2=CH-CH2_2-Cl is a/an: A) Vinylic halide *B) Allylic halide C) Aryl halide D) Tertiary halide Explanation: The halogen is attached to an sp3^3 carbon adjacent to a C=C bond, so it is allylic.

Q21. SN2 stereochemistry is: A) Retention *B) Inversion C) Racemisation D) No change Explanation: SN2 occurs by backside attack and gives inversion of configuration.

Q22. Freon-12 has the formula: A) CCl4_4 B) CHCl3_3 *C) CCl2_2F2_2 D) CH2_2Cl2_2 Explanation: Freon-12 is dichlorodifluoromethane, CCl2_2F2_2.

Q23. 2-bromopropane + aqueous KOH gives: A) Propene *B) Propan-2-ol C) Propane D) Propyne Explanation: Aqueous KOH favours nucleophilic substitution, giving propan-2-ol.

Q24. Grignard reagent has the formula: A) R-Na *B) RMgX C) R-R D) R-OH Explanation: Grignard reagents are alkyl or aryl magnesium halides, RMgX.

Q25. The IUPAC name of CHCl3_3 is: A) chloroform *B) trichloromethane C) carbon trichloride D) methyl chloride Explanation: CHCl3_3 is named trichloromethane in IUPAC nomenclature.

Q26. Reactivity of alcohols with HX: A) 1 > 2 > 3 degree *B) 3 > 2 > 1 degree C) 2 > 3 > 1 D) All equal Explanation: Tertiary alcohols generally react fastest with HX, followed by secondary and then primary alcohols.