Assertion Reason Questions for Class 11 Chemistry Chapter 13 Hydrocarbons
Directions: (a) Assertion and reason both are correct statements and reason is correct explanation for assertion.
(b) Assertion and reason both are correct statements but reason is not correct explanation for assertion.
(c) Assertion is correct statement but reason is wrong statement.
(d) Assertion is wrong statement but reason is correct statement.
Q.1. Assertion : Acetylene is acidic in nature.
Reason : Acetylene is sp hybridised.
AnswerAnswer:(b) : The acidic nature in acetylene is described on the basis of higher electronegativity of sp hybridized carbon atom which pulls the C – H bond pair more effectively to lose H+.
Q.2. Assertion : Boiling point of alkanes increases with increase in molecular weight.
Reason : van der Waal’s forces increase with increase in molecular weight.
AnswerAnswer:(a) : Greater is the molecular mass, greater is the magnitude of van der Waal’s forces of attraction and hence higher the boiling point.
Q.3. Assertion : Benzene on heating with conc. H2SO4 gives benzene sulphonic acid which when heated with superheated steam under pressure gives benzene.
Reason : Sulphonation is a reversible process.
AnswerAnswer:(a) : Sulphonation of benzene is an electrophilic substitution reaction in which SO3 acts as the electrophile.
Q.4. Assertion : Sodium acetate on Kolbe’s electrolysis gives methane.
Reason : Methyl free radical is formed at anode.
AnswerAnswer:(d) : Sodium acetate on Kolbe’s electrolysis gives ethane. It is formed at anode.
Q.5. Assertion : Trans-pent-2-ene is polar but trans-but-2-ene is non-polar.
Reason : The polarity of cis-isomer is more than trans which are either non-polar or less polar.
AnswerAnswer:(b) : The vector sum of all polar bonds in trans-pent-2- ene is not zero but the vector sum is zero in trans-but-2-ene.
Q.6. Assertion : HC ≡ C– is more stable than H2C = CH–.
Reason : HC ≡ C– has more s-character than H2C = CH–.
AnswerAnswer:(a) : HC ≡ C– has 50% s-character and H2C = CH– has 33% s-character. Stability of carbanions increases with an increase in the s-character at the carbanion. So, HC ≡ C– is more stable than H2C = CH–.
Q.7. Assertion : All the hydrogen atoms in CH2 =C= CH2 are attached to sp2 hybridised carbon atom.
Reason : All the carbon atoms in its are sp2 hybridized.
AnswerAnswer:(c) : The two H-atom on first carbon and the two H-atoms on the third carbon atom are attached to sp2 hybridised carbon atoms. The central carbon atom is sp-hybridized.
Q.8. Assertion : Methane cannot be obtained by Wurtz reaction.
Reason : Wurtz reaction leads to the formation of symmetrical alkane having an even number of carbon atoms.
AnswerAnswer:(a) : Wurtz reaction involves the formation of alkanes by heating alkyl halide with sodium in ether. In this reaction two alkyl radicals join together to form an alkane. The net result in this reaction is the formation of symmetrical alkane (R–R) having an even number of carbon atoms.
Q.9. Assertion : Saturated hydrocarbons are chemically less reactive.
Reason : All isomeric paraffins have same parent name.
AnswerAnswer:(c) : Less reactivity of saturated hydrocarbons is due to the presence of single bonds between carbon atoms. Paraffins (alkanes) may have straight chain or branched chain isomers which have different parent names.
Q.10. Assertion : Nitrobenzene does not undergo Friedel Crafts reaction.
Reason : Nitrobenzene is a m-director.