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NEET Chemistry MCQ
Hydrocarbons Mcq Neet Chemistry
Quiz 9
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Q.1
Which one of the following compounds would have the highest heat ofhydrogenation? [ JIPMER1998]
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a) CH2 = CH2
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b) CH3 - CH2 - CH = CH2
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c) CH3CH = CHCH3
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d) (CH3)2C = C(CH3)2
Explanation
Least substituted alkene has highest heat of hydration Answer:(a)
Q.2
Which of the following compounds can yiled only one monochlorinated product upon free radical chlorination [ PMT Kerala 2011]
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a) 2,2-Dimethylpropane
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b) 2-Methylpropane
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c) 2-Methylbutane
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d) Propane
Explanation
Answer:(a)
Q.3
The intermediate during the addition of HCl to propene in the presence of peroxide is ... [ IIT 1997]
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a)
0%
b)
0%
c)
0%
d)
Explanation
Peroxide effect (or free radical addition) occurs only in case of HBr. The addition of HCl in presence or absence of peroxides occurs by an ionic mechanism. Addition of H+ gives more stable carbocation as the intermediate. Answer:(b)
Q.4
In the presence of peroxide, hydrogen chloride and hydrogen iodide do not give anti-Markownikoff's addition to alkeens because ...[ IIT 2001]
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a) both are highly ionic
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b) one is oxidising and the other is reducing
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c) one of the steps is endothermic in both the cases
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d) all the steps are exothermic in both the cases
Explanation
In addition of HBr to an alkene, in the presence of peroxide, both the propagation steps are exothermic HBr + HO* → H2O + Br* Propogation CH3 - CH = CH2 + Br* → CH3 - C*H - CH2Br ΔH < 0 CH3-C*H - CH2Br + HBr → CH3 - CH2 - CH2Br + Br*; ΔH < 0 In case of addition of HCl and HI one of the propagation step is endothermic, reaction fail to occur Answer:(c)
Q.5
In Friedel-Crafts alkylation,besidesAlCl3, the other reactants are...[ CBSE PMT 1999]
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a) C6H6 + NH3
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b) C6H6 + CH4
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c) C6H6 + CH3Cl
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d) C6H6 + CH3COCl
Explanation
Answer:(c)
Q.6
Anti-markovnikov's addition of HBr is not observed in ... [ IIT 1985]
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a) Propene
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b) 1-Butene
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c) But-2-ene
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d) Pent-2-ene
Explanation
Anti-markovnikov's addition of HBr is observed only with unsymmetrical alkenes But-2-ene is symmetrical Answer:(c)
Q.7
Which of the following will be most easily attacked by an electrophile? [ MP PMT 2004]
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a)
0%
b)
0%
c)
0%
d)
Explanation
Answer:(c)
Q.8
on Q251) Which is a pair of geometrical isomers? [ DPMT 2002]
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a) I and II
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b) I and III
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c) II and IV
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d) III and IV
Explanation
Each doubly bond carbon atoms is attached to two different atoms or group Answer:(c)
Q.9
1-chlorobutane,on reaction with alcoholic potash (KOH) gives ...[ AFMC 1998]
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a) 1-Butene
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b) 1-Butanol
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c) 2-Butene
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d) 2-Butanol
Explanation
Answer:(a)
Q.10
Reaction of acetylene and propylene with HgSO4 in presence of H2SO4 produces respectively ..[ BHU 2006]
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a) acetone and acetaldehyde
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b) acetaldehyde and acetone
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c) propanaldehyde and acetone
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d) acetone and propanaldehyde
Explanation
Answer:(b)
Q.11
The direct iodination of benzene is not possible because
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a) Iodine is an oxidising agent
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b) Resulting C6H5I is reduced to C6H6 by HI
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c) HI is unstable
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d) The ring gets deactivated
Explanation
Answer:(b)
Q.12
on Q284) Which of the following applies in the reaction (i) CH3CH = CHCH3 (major product) (ii) CH2=CH -CH2CH3(minor product)
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a) Markovnikov's rule
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b) Saytzeff's rule
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c) Kharasch effect
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d) Hofmann's rule
Explanation
Answer:(b)
Q.13
Which of the following isomeric heptanes can yield seven different monochlorinated products upon free radical chlorination ..[ PMT Kerala 2010]
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a) 2,3-dimethylpentane
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b) 2,2-dimethylpentane
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c) 3-methylhexane
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d) 2-methylhexane
Explanation
3-methylhexane can yield seven different monochlorinated products upon free radical chlorination as the chemical environment of all the seven carbon atoms is different Answer:(c)
Q.14
Chlorination of an alkane involves the attack of ... [ Pb CET 1990]
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a) An electrophile
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b) A nucleophile
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c) A base
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d) A free radical
Explanation
Answer:(d)
Q.15
The number of structural and configurational isomers of a bromo compound C5H9Br formed by the addition of HBr to 2-pentyne respectively, are ....[ IIT 1988]
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a) 1 and 2
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b) 2 and 4
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c) 4 and 2
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d) 2 and 1
Explanation
Answer:(b)
Q.16
ropyne on polymerization gives ...[ CPMT 1999]
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a) Mesitylene
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b) Propylbenzene
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c) Ethylbenzene
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d) Benzene
Explanation
Answer:(a)
Q.17
Which of the following compounds have lowest boiling point? [ CBSE 1994]
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a) CH3CH2CH2CH2CH3
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b) CH3CH = CHCH2CH3
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c) CH3CH = CH - CH - CH = CH2
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d) CH3CH2CH2CH3
Explanation
Lower the number of carbon atom lower is the boiling point Answer:(d)
Q.18
Marsh gas mainly contains ...[ IIT 1980]
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a) C2H2
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b) CH4
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c) H2S
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d) CO
Explanation
Methane is produced due to the decay of vegetable or animal organisms present in swamps and marsh, by the action of bacteria. Due to this method of formation, methane is also known as marsh gas. Answer:(b)
Q.19
1-butyne reacts with cold alkaline KMnO4 to produce ...[ AIIMS 1997]
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a) CH3CH2COOH
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b) CH3CH2CH2COOH
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c) CH3CH2COOH +CO2
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d) CH3CH2COOH + HCOOH
Explanation
Answer:(c)
Q.20
The products obtained viaoxymercuration(HgSO4 + H2SO4)of1-butyne would be ... [ IIT 1998]
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a) CH3- CH2- CO- CH3
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b) CH3 - CH2 - CH2 - CHO
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c) CH3 - CH2 - CHO + HCHO
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d) CH3CH2COOH + HCOOH
Explanation
Oxymercurationof terminal alkynes always gives methyl ketones as the major product Answer:(a)
Q.21
Propan - 1 -ol can be prepared from propene by ...[ AIIMS 2003]
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a) H2O/H2SO4
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b) B2H6 follwed by H2O2
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c) CH3COOH/ H2SO4
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d) Hg(OAC)2/ H2O followed by NaBH4
Explanation
Answer:(b)
Q.22
Ozonolysis of 1,3-dutadenegives ...[Haryana CEET 1999]
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a) Mixture of an aldehyde and a ketone
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b) Mixture of an aldehyde and an acid
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c) only aldehyde
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d) only ketone
Explanation
Answer:(c)
Q.23
The most reactive hydrocarbon is ...[ JIPMER 2003]
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a) ethene
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b) ethyne
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c) ethane
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d) methane
Explanation
Theπ-bond is weaker than a sigma bond and is easily brocken, hence alkenes or alkynes are more reactive than alkanes. Due to greater electronegativity of spp-hybridized carbon of triple bond than sp2-hybridized carbonm atom of double bond, the π-electrons in alkenes and hence are less easily available for addition reaction with electrophiles. therefore, alkenes (ethene) is most reactive hydrocarbon Answer:(a)
Q.24
Which of the following will have fastest rate of reaction with Br2/FeBr3 [AMU 1997]
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a)
0%
b)
0%
c)
0%
d)
Explanation
-OCH3 group is a stronger electron-donating group than CH3 group, therefore, C6H5-OCH3 has the fastest rate of reaction with Br2/FeBr3 Answer:(d)
Q.25
Which ofthe following compound gives similar products obeying Markovnikov'srule and peroxideeffect? [ Rajasthan PMT1998]
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a) CH3 - CH = CH2
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b) CH3CH = CH -CH3
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c) C2H5-CH = CH - CH3
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d) C2H5- CH = CH2
Explanation
Symmetricalalene gives the same product obeying Markovnikov's rule and peroxide effect Answer:(b)
Q.26
on Q268) IDentify X infollowing reaction
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a)
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b)
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c)
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d)
Explanation
Br free radical is less reactive but more selective, therefor it will produce more stable 3° free radical Which is option "b" Answer:(b)
Q.27
An example of electrophilic substitution reaction is ...[ CBSE PMT 1994]
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a) Chlorinqation of methane
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b) Conversion of methyl chloride to methyl alcohol
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c) Nitration of benzene
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d) Formation of ethylene from ethyl alcohol
Explanation
Answer:(c)
Q.28
CH3 - CH = CH2 + NOCl → P; Identify the adduct ...[ IIT 2006]
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a)
0%
b)
0%
c)
0%
d)
Explanation
NOCl undergo electrophilic addition on alkene as NOCl → +N = O + Cl- Answer:(a)
Q.29
The major product formed when 2-bromobutane is treated with alcoholic KOH is ...[ PMT kerala 2010]
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a) 2-butanol
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b) trans-2-butene
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c) 1-butanol
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d) 1-butene
Explanation
Answer:(b)
Q.30
MEthane is formed when ... [ AFMC 1987]
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a) Sodium acetate is heated with soda lime
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b) Iodomethane is reduced
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c) Aluminium carbide reactswwith water
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d) All of the above
Explanation
a) CH3COONa + NaOH → CH4 + Na2CO3 Soda lime is mixture of NaOh + CaO b) CH3I on reduction give CH4 c) Al4C3 + 12H2O → 4Al(OH)3 + 3CH4 Answer:(d)
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