chemistry MCQs - 12th class Chapter 09 Mcqs

1

The term 'aromatic' is derived from the Greek word 'aroma', which means?

A

Sweet

B

Fragrant

C

Odourless

D

Colourful

2

Which of the following is recognized as the simplest and parent member of aromatic hydrocarbons?

A

Naphthalene

B

Toluene

C

Benzene

D

Phenol

3

Aromatic hydrocarbons containing one benzene ring in their molecules are called?

A

Polycyclic

B

Monocyclic

C

Alicyclic

D

Acyclic

4

Polycyclic aromatic hydrocarbons in which benzene rings are fused together at ortho positions are exemplified by?

A

Biphenyl

B

Diphenylmethane

C

Naphthalene

D

Toluene

5

The molecular mass of benzene is 78.108, which is how many times its empirical formula mass (13)?

A

4

B

5

C

6

D

7

6

A group obtained by removing a hydrogen atom from a benzene molecule is called?

A

Aryl group

B

Alkyl group

C

Phenyl group

D

Benzyl group

7

When two substituents are on adjacent carbon atoms (positions 1,2) in a benzene ring, it is called the?

A

meta-isomer

B

para-isomer

C

ortho-isomer

D

cis-isomer

8

Which of the following functional groups has the highest priority in IUPAC nomenclature for benzene derivatives?

A

-OH

B

-CHO

C

-NH2

D

-COOH

9

Benzene was discovered by Michael Faraday in which year?

A

1865

B

1845

C

1825

D

1930

10

The observation that benzene gives only one monosubstituted product supports its?

A

Straight chain structure

B

Unsaturated nature

C

Saturated nature

D

Cyclic hexagonal structure

11

The molecular formula of benzene, C6H6, does not correspond to which general formula for open-chain hydrocarbons?

A

Alkane (CnH2n+2)

B

Alkene (CnH2n)

C

Alkyne (CnH2n-2)

D

All of the above

12

Who proposed the cyclic regular hexagonal structure for benzene in 1865?

A

Faraday

B

Hoffmann

C

Kekule

D

Dewar

13

The reaction of benzene with 3 molecules of H2 in the presence of a catalyst to form cyclohexane confirms the presence of?

A

One double bond

B

Two double bonds

C

Three double bonds

D

A stable ring

14

According to X-ray studies, all C-C-C bond angles in benzene are?

A

109.5°

B

90°

C

180°

D

120°

15

What is the C-C bond length in a benzene molecule?

A

1.54 Å

B

1.34 Å

C

1.397 Å

D

1.20 Å

16

In the atomic orbital treatment of benzene, each carbon atom is?

A

sp hybridized

B

sp2 hybridized

C

sp3 hybridized

D

unhybridized

17

The stability of benzene is attributed to the extensive delocalization of which electrons?

A

sigma electrons

B

pi electrons

C

s-orbital electrons

D

lone pair electrons

18

The heat of hydrogenation for cyclohexene is?

A

-208 kJ/mol

B

-119.5 kJ/mol

C

-231.5 kJ/mol

D

-358.5 kJ/mol

19

The resonance energy of benzene, calculated from the difference in expected and observed heats of hydrogenation, is?

A

208 kJ/mol

B

119.5 kJ/mol

C

358.5 kJ/mol

D

150.5 kJ/mol

20

The C-C bond length in benzene is intermediate between that of an alkane and an?

A

Alkyne

B

Alkene

C

Cycloalkane

D

Aromatic ion

21

Benzene can be prepared from n-hexane using Cr2O3 + Al2O3 + SiO2 as catalysts at what temperature?

A

100°C

B

250°C

C

500°C

D

70°C

22

The polymerization of acetylene to benzene occurs at 70°C over which catalyst?

A

Pt or Pd

B

Organo-nickel catalyst

C

AlCl3

D

V2O5

23

Heating sodium benzoate with what substance produces benzene?

A

Zinc dust

B

Soda lime

C

Dilute HCl

D

n-Hexane

24

The Wurtz-Fittig reaction is used for the synthesis of?

A

Alkanes only

B

Phenols

C

Alkyl aromatic hydrocarbons

D

Ketones

25

In electrophilic substitution of benzene, what is the role of a catalyst like FeX3?

A

To attack the benzene ring directly

B

To form a stable intermediate

C

To produce a powerful electrophile

D

To stabilize the pi-electron cloud

26

The introduction of a halogen group into the benzene ring is called?

A

Nitration

B

Sulphonation

C

Alkylation

D

Halogenation

27

In the halogenation of benzene, what is the actual electrophile that attacks the ring?

A

Cl2

B

FeCl3

C

Cl+

D

Cl-

28

For the nitration of benzene, a mixture of concentrated HNO3 and concentrated H2SO4 is used at what temperature range?

A

0-10°C

B

20-30°C

C

50-55°C

D

95-100°C

29

The active nitrating agent in the nitration of benzene is the?

A

Nitrate ion (NO3-)

B

Nitrite ion (NO2-)

C

Nitronium ion (NO2+)

D

Nitric acid molecule (HNO3)

30

The electrophile in the sulphonation of benzene using concentrated H2SO4 is?

A

H2SO4

B

HSO4-

C

SO3

D

H3O+

31

The introduction of an alkyl group into the benzene ring using an alkyl halide and AlCl3 is called?

A

Friedel-Crafts Acylation

B

Wurtz-Fittig Reaction

C

Friedel-Crafts Alkylation

D

Halogenation

32

What is the product of the reaction between benzene and acetyl chloride (CH3COCl) in the presence of AlCl3?

A

Toluene

B

Acetophenone

C

Benzoyl chloride

D

Ethylbenzene

33

The reduction of benzene with H2 in the presence of Pt yields?

A

Hexane

B

Cyclohexene

C

Cyclohexane

D

1,3-Cyclohexadiene

34

The reaction of benzene with Cl2 in the presence of sunlight results in an?

A

Substitution reaction

B

Addition reaction

C

Elimination reaction

D

Oxidation reaction

35

Catalytic oxidation of benzene with V2O5 at 450°C yields?

A

Benzoic acid

B

Phenol

C

Maleic anhydride

D

Glyoxal

36

The ozonolysis of benzene, followed by hydrolysis, gives?

A

Glyoxal

B

Maleic acid

C

Formic acid

D

Benzaldehyde

37

Side-chain oxidation of ethylbenzene with acidified KMnO4 produces?

A

Phenol

B

Benzoic acid

C

Acetophenone

D

Benzaldehyde

38

In electrophilic substitution, an -OH group on the benzene ring directs incoming groups to which positions?

A

meta only

B

ortho and meta

C

meta and para

D

ortho and para

39

Which of the following is a meta-directing group?

A

-NH2

B

-Cl

C

-CH3

D

-NO2

40

Ortho- and para-directing groups are said to be what type of groups?

A

Deactivating

B

Activating

C

Neutral

D

Electron-withdrawing

41

Compared to alkenes, benzene is?

A

More reactive towards electrophiles

B

Less reactive towards electrophiles

C

Equally reactive

D

Only reactive with nucleophiles

42

The substitution of a second nitro group into nitrobenzene occurs at 95°C, yielding mainly?

A

o-Dinitrobenzene

B

p-Dinitrobenzene

C

m-Dinitrobenzene

D

A mix of all three

43

The conversion of n-hexane into benzene by heating in the presence of a catalyst is an example of?

A

Isomerization

B

Dealkylation

C

Aromatization

D

Rearrangement

44

Which compound is the most reactive towards electrophilic nitration?

A

Benzene

B

Nitrobenzene

C

Toluene

D

Benzoic acid

45

In the Friedel-Crafts reaction, which catalyst is commonly used?

A

H2SO4

B

HNO3

C

AlCl3

D

KMnO4

46

Aromatic compounds typically burn with a sooty flame because they have a?

A

High percentage of hydrogen

B

Ring structure

C

High percentage of carbon

D

Resistance to reaction with air

47

Which of the following is an example of a polycyclic aromatic hydrocarbon with isolated rings?

A

Naphthalene

B

Anthracene

C

Phenanthrene

D

Biphenyl

48

The complete combustion of benzene (C6H6) in excess air produces CO2 and?

A

H2

B

CO

C

H2O

D

C

49

When toluene is treated with chlorine in the presence of sunlight, substitution occurs on the?

A

Benzene ring

B

Methyl group

C

Ortho position

D

Para position

50

Benzene is a very stable molecule due to its?

A

Planar structure

B

Six carbon atoms

C

Resonance energy

D

High C:H ratio