Q26 of 30 Page 188

Assertion (A): Nitration of benzene requires the use of concentrated sulphuric acid and nitric acid.

Reason (R): The mixture of acids produces the electrophile for the reaction.


A. A and R both are correct but R is not the explanation of A.


B. A is false but R is correct.


C. A and R both are correct and R is the correct explanation of A.


D. A and R both are incorrect.


C. A and R both are correct and R is the correct explanation of A.


A nitro group can be introduced into the benzene ring by heating benzene with a mixture of concentrated nitric acid and concentrated sulphuric acid which is called nitrating mixture.


This nitrating mixture forms a very good electrophile called nitronium ion and then it attacks on benzene ring to form nitrobenzene.


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24

Give the reactions involved in the preparation of propane from the following :

(i) CH3—CH = CH2


(ii) CH3 CH2 CH2 Cl


(iii) CH3 CH2 CH2 COO– Na+


 25

Assertion (A) : The first ionization enthalpy of alkali metals decreases down the group.

Reason (R) : Increase in number of orbitals increases the shielding effect which outweighs the increasing nuclear charge, therefore, the removal of outermost electron requires less energy on moving down the group.


A. A and R both are correct but R is not the explanation of A.


B. A is false but R is correct.


C. A and R both are correct and R is the correct explanation of A.


D. A and R both are incorrect.


 27

Assertion (A) : Ozone is destroyed by solar radiations in upper stratosphere.

Reason (R) : Thinning of ozone layer allows excessive UV radiations to reach the surface of earth.


A. A and R both are correct but R is not the explanation of A.


B. A is false but R is correct.


C. A and R both are correct and R is the correct explanation of A.


D. A and R both are incorrect.


 28

(a) Liquids can be considered as very dense gases. When a liquid phase changes to gas phase, the liquid and the gas phases are in equilibrium and a surface separates the two phases. This surface is visible if both phases are in equilibrium and are below critical tempertaure and pressure. However, it is possible to interconvert liquid and gas wherein two phases are never present together.

With the help of a well-labelled diagram show that CO2 gas can be liquified by changing the pressure and temperature without passing through the situation when both gaseous and liquid CO2 are at equilibrium.


(b) Arrange the following liquids in increasing order of their viscosities. Give reason for your answer.


Water, benzene, ethane-1,2-diol.