Instructions
- All 45 questions are compulsory. Each question carries 4 marks; 1 mark is deducted for every wrong answer.
- Each question has four options, of which only one is correct.
- Questions 40–42 are Assertion–Reason type and questions 43–45 are Match-the-following type.
- Use of calculators, log tables and mobile phones is not permitted.
- Attempt the paper in one sitting under exam conditions and mark answers on a separate sheet before checking the key.
SECTION A — Multiple Choice Questions (Q1 – Q39)
1. According to Huckel's rule, a planar cyclic conjugated system is aromatic if the number of delocalised π electrons is| (a) 4n | (b) (4n + 2) |
| (c) (2n + 4) | (d) 2n |
2. Which of the following species is aromatic?| (a) Cyclooctatetraene | (b) Cyclopentadienyl cation |
| (c) Cycloheptatrienyl (tropylium) cation | (d) Cyclobutadiene |
3. All the six carbon–carbon bonds in benzene are of equal length (139 pm). This is best explained by| (a) sp3 hybridisation of carbon | (b) Resonance / complete delocalisation of π electrons |
| (c) Hyperconjugation of C–H bonds | (d) The –I effect of hydrogen |
4. The hybridisation of each carbon atom and the C–C–C bond angle in benzene are respectively| (a) sp3, 109°28' | (b) sp2, 120° |
| (c) sp, 180° | (d) sp2, 109°28' |
5. The resonance energy of benzene is approximately| (a) 36 kJ mol–1 | (b) 150 kJ mol–1 |
| (c) 358 kJ mol–1 | (d) 640 kJ mol–1 |
6. Benzene prefers electrophilic substitution over addition reactions because| (a) It contains six hydrogen atoms | (b) Substitution preserves the delocalised aromatic sextet while addition destroys it |
| (c) It is a saturated hydrocarbon | (d) Its carbon atoms are sp hybridised |
7. Cyclic polymerisation of ethyne when passed through a red hot iron tube at 873 K gives| (a) Ethene | (b) Benzene |
| (c) Cyclooctatetraene | (d) Naphthalene |
8. Benzene is obtained when sodium benzoate is heated with| (a) Concentrated H2SO4 | (b) Soda lime (NaOH + CaO) |
| (c) Zn dust | (d) Cu tube at 573 K |
9. Phenol on distillation with zinc dust yields| (a) Cyclohexanol | (b) Benzene |
| (c) Benzoic acid | (d) Toluene |
10. The electrophile that attacks the benzene ring during nitration with a mixture of conc. HNO3 and conc. H2SO4 is| (a) NO2– | (b) NO+ |
| (c) NO2+ | (d) HNO3 itself |
11. The reaction of benzene with fuming sulphuric acid to give benzenesulphonic acid is| (a) Irreversible and involves SO3 as the electrophile | (b) Reversible and involves SO3 as the electrophile |
| (c) Reversible and involves SO42– as the electrophile | (d) A nucleophilic substitution |
12. Friedel–Crafts alkylation of benzene with methyl chloride is carried out in the presence of| (a) Anhydrous AlCl3 | (b) Aqueous NaOH |
| (c) Alcoholic KOH | (d) Ni at 573 K |
13. Benzene reacts with acetyl chloride in presence of anhydrous AlCl3 to give| (a) Toluene | (b) Acetophenone |
| (c) Benzoic acid | (d) Benzaldehyde |
14. Which of the following does not undergo the Friedel–Crafts reaction?| (a) Benzene | (b) Toluene |
| (c) Chlorobenzene | (d) Nitrobenzene |
15. Benzene reacts with chlorine in the presence of bright sunlight (UV light) in absence of a halogen carrier to give| (a) Chlorobenzene | (b) Benzene hexachloride (gammexane) |
| (c) Benzyl chloride | (d) Hexachlorobenzene |
16. The number of moles of hydrogen required to convert one mole of benzene into cyclohexane in presence of Ni at 473–573 K is
17. Ozonolysis of benzene followed by hydrolysis with Zn/H2O gives| (a) Three molecules of glyoxal | (b) Three molecules of formaldehyde |
| (c) Two molecules of glyoxal and one of formaldehyde | (d) Benzoic acid |
18. Toluene on oxidation with hot alkaline KMnO4 followed by acidification gives| (a) Benzaldehyde | (b) Benzoic acid |
| (c) Benzyl alcohol | (d) Phenol |
19. Toluene reacts with Cl2 in presence of sunlight to give mainly| (a) o- and p-chlorotoluene | (b) Benzyl chloride |
| (c) Benzoyl chloride | (d) Benzene hexachloride |
20. Toluene reacts with Cl2 in presence of anhydrous FeCl3 to give| (a) Benzyl chloride | (b) o- and p-chlorotoluene |
| (c) m-chlorotoluene | (d) Benzal chloride |
21. Which of the following groups is deactivating but ortho, para-directing?| (a) –NO2 | (b) –Cl |
| (c) –CH3 | (d) –OH |
22. Which of the following is the strongest activating group towards electrophilic substitution?| (a) –CH3 | (b) –Cl |
| (c) –NH2 | (d) –COOH |
23. Which one of the following is a meta-directing group?| (a) –OCH3 | (b) –NHCOCH3 |
| (c) –COOH | (d) –CH3 |
24. The correct order of reactivity towards electrophilic substitution is| (a) Anisole > toluene > benzene > chlorobenzene | (b) Chlorobenzene > benzene > toluene > anisole |
| (c) Benzene > toluene > anisole > chlorobenzene | (d) Toluene > anisole > chlorobenzene > benzene |
25. Nitration of nitrobenzene with conc. HNO3 and conc. H2SO4 at 373 K gives mainly| (a) o-dinitrobenzene | (b) m-dinitrobenzene |
| (c) p-dinitrobenzene | (d) 1,3,5-trinitrobenzene |
26. The number of possible isomeric dichlorobenzenes is
27. The number of possible aromatic isomers with molecular formula C8H10 is
28. The number of possible isomeric trichlorobenzenes is
29. Benzene does not decolourise bromine water. This is because| (a) Benzene is insoluble in water | (b) Benzene does not readily undergo addition reactions owing to the delocalised π sextet |
| (c) Bromine water is a weak reagent | (d) Benzene reacts only with Cl2 |
30. Chlorobenzene on treatment with methyl chloride and sodium in dry ether gives toluene. This reaction is called| (a) Fittig reaction | (b) Wurtz–Fittig reaction |
| (c) Etard reaction | (d) Sandmeyer reaction |
31. Two molecules of bromobenzene on treatment with sodium in dry ether give| (a) Benzene | (b) Biphenyl |
| (c) Toluene | (d) Naphthalene |
32. Which of the following polynuclear hydrocarbons is a well known carcinogen?| (a) Naphthalene | (b) Biphenyl |
| (c) Benzo(a)pyrene | (d) Toluene |
33. The number of delocalised π electrons in naphthalene is
34. Sulphonation of naphthalene at 353 K gives mainly| (a) Naphthalene-1-sulphonic acid | (b) Naphthalene-2-sulphonic acid |
| (c) Naphthalene-1,5-disulphonic acid | (d) No reaction |
35. The intermediate formed when an electrophile attacks the benzene ring is| (a) A free radical | (b) A carbanion |
| (c) An arenium ion (sigma complex) that is resonance stabilised | (d) A carbene |
36. Toluene reacts with chromyl chloride (CrO2Cl2) in CS2 followed by hydrolysis to give benzaldehyde. This reaction is known as| (a) Etard reaction | (b) Gattermann–Koch reaction |
| (c) Reimer–Tiemann reaction | (d) Kolbe reaction |
37. Benzene treated with carbon monoxide and HCl in presence of anhydrous AlCl3/CuCl gives benzaldehyde. This is the| (a) Etard reaction | (b) Gattermann–Koch reaction |
| (c) Wurtz–Fittig reaction | (d) Friedel–Crafts alkylation |
38. Aromatic hydrocarbons burn with a sooty (luminous) flame because| (a) They have a low carbon percentage | (b) They have a high carbon to hydrogen ratio |
| (c) They contain oxygen | (d) They are saturated |
39. The essential conditions for a compound to be aromatic are| (a) Planarity, cyclic delocalisation and (4n+2) π electrons | (b) Planarity and sp3 hybridisation |
| (c) Only the presence of a benzene ring | (d) Cyclic structure and 4n π electrons |
SECTION B — Assertion and Reason (Q40 – Q42)
In the following questions, a statement of Assertion (A) is followed by a statement of Reason (R). Choose the correct option.
40. Assertion (A): Benzene undergoes electrophilic substitution reactions much more readily than addition reactions.
Reason (R): Substitution regenerates the delocalised aromatic sextet, whereas addition would destroy it.
| (a) Both A and R are true and R is the correct explanation of A |
| (b) Both A and R are true but R is not the correct explanation of A |
| (c) A is true but R is false |
| (d) A is false but R is true |
41. Assertion (A): Nitration of nitrobenzene requires more drastic conditions than nitration of benzene.
Reason (R): The nitro group withdraws electron density from the ring through –I and –R effects.
| (a) Both A and R are true and R is the correct explanation of A |
| (b) Both A and R are true but R is not the correct explanation of A |
| (c) A is true but R is false |
| (d) A is false but R is true |
42. Assertion (A): Cyclooctatetraene is aromatic in nature.
Reason (R): Cyclooctatetraene contains eight π electrons in a cyclic system.
| (a) Both A and R are true and R is the correct explanation of A |
| (b) Both A and R are true but R is not the correct explanation of A |
| (c) A is true but R is false |
| (d) A is false but R is true |
SECTION C — Match the Following (Q43 – Q45)
43. Match the reagent/condition used with benzene in Column I with the product in Column II.| Column I | Column II |
|---|
| A. CH3COCl / anhydrous AlCl3 | i. Cyclohexane |
| B. H2 / Ni, 473–573 K | ii. Benzenesulphonic acid |
| C. Fuming H2SO4, Δ | iii. Acetophenone |
| D. Cl2 / UV light | iv. Benzene hexachloride |
| (a) A-iii, B-i, C-ii, D-iv |
| (b) A-i, B-iii, C-iv, D-ii |
| (c) A-iii, B-ii, C-i, D-iv |
| (d) A-iv, B-i, C-ii, D-iii |
44. Match the name reaction in Column I with the organic product in Column II.| Column I | Column II |
|---|
| A. Etard reaction (on toluene) | i. Biphenyl |
| B. Fittig reaction (on bromobenzene) | ii. Ethylbenzene |
| C. Wurtz–Fittig reaction (chlorobenzene + CH3Cl) | iii. Benzaldehyde |
| D. Friedel–Crafts alkylation (benzene + C2H5Cl) | iv. Toluene |
| (a) A-iii, B-i, C-iv, D-ii |
| (b) A-i, B-iii, C-ii, D-iv |
| (c) A-iii, B-iv, C-i, D-ii |
| (d) A-ii, B-i, C-iv, D-iii |
45. Match the substituent in Column I with its influence on electrophilic substitution in Column II.| Column I | Column II |
|---|
| A. –NH2 | i. Weakly activating, o/p-directing |
| B. –Cl | ii. Deactivating, o/p-directing |
| C. –NO2 | iii. Strongly deactivating, m-directing |
| D. –CH3 | iv. Strongly activating, o/p-directing |
| (a) A-iv, B-ii, C-iii, D-i |
| (b) A-i, B-ii, C-iii, D-iv |
| (c) A-iv, B-iii, C-ii, D-i |
| (d) A-ii, B-iv, C-iii, D-i |
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