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NCERT Solutions for class 11 Chemistry | Chapter 13 : Hydrocarbons

(1) Assertion (A) : Toluene on Friedal Crafts methylation gives o– and p–xylene.

Reason (R) : CH3-group bonded to benzene ring increases electron density at o– and p– position.

[A] Both A and R are correct and R is the correct explanation of A.
[B] Both A and R are correct but R is not the correct explanation of A.
[C] Both A and R are not correct.
[D] A is not correct but R is correct.
Answer: Both A and R are correct and R is the correct explanation of A.
(2) Assertion (A) : Nitration of benzene with nitric acid requires the use of concentrated sulphuric acid.

Reason (R) : The mixture of concentrated sulphuric acid and concentrated nitric acid produces the electrophile, NO2+ .

[A] Both A and R are correct and R is the correct explanation of A.
[B] Both A and R are correct but R is not the correct explanation of A.
[C] Both A and R are not correct.
[D] A is not correct but R is correct.
Answer: Both A and R are correct and R is the correct explanation of A.

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(3) Assertion (A) : Among isomeric pentanes, 2, 2-dimethylpentane has highest boiling point.

Reason (R) : Branching does not affect the boiling point.

[A] Both A and R are correct and R is the correct explanation of A.
[B] Both A and R are correct but R is not the correct explanation of A.
[C] Both A and R are not correct.
[D] A is not correct but R is correct.
Answer: Both A and R are not correct.
(4) Arrange the following hydrogen halides in order of their decreasing reactivity with propane.
[A] HCl > HBr > HI
[B] HBr > HI > HCl
[C] HI > HBr > HCl
[D] HCl > HI > HBr
Answer: HI > HBr > HCl
(5) The increasing order of reduction of alkyl halides with zinc and dilute HCl is
[A] R–Cl < R–I < R–Br
[B] R–Cl < R–Br < R–I
[C] R–I < R–Br < R–Cl
[D] R–Br < R–I < R–Cl
Answer: R–Cl < R–Br < R–I
(6) Arrange the halogens F2 , Cl2 , Br2 , I2 , in order of their increasing reactivity with alkanes.
[A] I2 < Br2 < Cl2 < F2
[B] Br2 < Cl2 < F2 < I2
[C] F2 < Cl2 < Br2 < I2
[D] Br2 < I2< Cl2 < F2
Answer: I2 < Br2 < Cl2 < F2
(7) Arrange the following in decreasing order of their boiling points.

(A) n–butane (B) 2–methylbutane

(C) n-pentane (D) 2,2–dimethylpropane

[A] A > B > C > D
[B] B > C > D > A
[C] D > C > B > A
[D] C > B > D > A
Answer: C > B > D > A
(8) A compound having a bond angle 180° is
[A] alkyne
[B] alkane
[C] alkene
[D] cycloalkane
Answer: alkyne
(9) C6H5CHO is formed when C6H6 is treated with CO and HCl in the presence of anhydrous AlCl3. Name of the reaction is:
[A] Friedel crafts reaction
[B] Gattermann Koch reaction
[C] Rosenmund reaction
[D] Stephen reaction
Answer: Gattermann Koch reaction
(10) Isopropyl iodide is formed after reaction of propene with HI, this is due to
[A] more stable free radical
[B] homolysis
[C] more stable carbanion
[D] more stable carbocation
Answer: more stable carbocation
(11) Which among the following reagent can be used to distinguish between CH2BrCH=CH2 from CH3CH=CHBr?
[A] Br2/CCl4
[B] cold KMnO4
[C] AgNO3/C2H5OH
[D] Ag(NH3)2OH
Answer: AgNO3/C2H5OH
(12) Which one of the following compound forms salt on reaction with NaNH2?
[A] C2H2
[B] C2H6
[C] C6H6
[D] C2H4
Answer: C2H2
(13) Which one of the following halide can be used in the Friedel-Crafts reaction?
[A] Isopropyl chloride
[B] Bromobenzene
[C] Chlorobenzene
[D] Chloroethene
Answer: Isopropyl chloride
(14) Choose the process by which liquid hydrocarbons can be converted to gaseous hydrocarbons
[A] hydrolysis
[B] oxidation
[C] cracking
[D] distillation under reduced pressure
Answer: cracking
(15) The product obtained on heating 2-Bromopentane with potassium ethoxide in ethanol is
[A] 1-pentene
[B] 2-cis-pentene
[C] trans-2-pentene
[D] 2-ethoxy pentane
Answer: trans-2-pentene
(16) Identify Z in the given reaction:

[A] (a)
[B] (b)
[C] (c)
[D] (d)
Answer: (d)
(17) Find the correct order of increasing acidity

[A] (a)
[B] (b)
[C] (c)
[D] (d)
Answer: (d)
(18) Among the following compounds the one that is most reactive towards electrophilic nitration is
[A] Toluene
[B] Benzene
[C] Benzoic Acid
[D] Nitrobenzene
Answer: Toluene
(19) Which branched chain isomer of the hydrocarbon with molecular mass 72u gives only one isomer of mono substituted alkyl halide?
[A] Tertiary butyl chloride
[B] Neopentane
[C] Isohexane
[D] Neohexane
Answer: Neopentane
(20) Ethyl benzene CANNOT be prepared by ______.
[A] Clemmensen reduction
[B] Wurtz reaction
[C] Wurtz-Fittig reaction
[D] Friedel-Crafts reaction
Answer: Wurtz reaction

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