Chemistry MCQs for NEET — Practice Questions with Answers

 Nitro group being electron withdrawing deactivates the benzene nucleus to such as extent so that it becomes incapable to give Fridel-Crafts reaction.

Nitrobenzene because of its unreactivity towards Friedel-Craft's reaction is used as a solvent for this reaction.

Key Idea Lower hydrocarbons exist in gaseous state while higher ones are in liquid state or solid state. On cracking or pyrolysis, the hydrocarbon with higher molecular mass gives a mixture of hydrocarbons having lower molecular mass. Hence, we can say that by cracking a liquid hydrocarbon can be converted into a mixture of gaseous hydrocarbons.

Key Idea Proton donor are acids and proton acceptor are bases.
Conc. H₂SO₄ and conc HNO₃, react in the following manner:

$$\begin{gathered} {\mathrm{HNO}}_3 + {\mathrm{H}}_2{\mathrm{SO}}_4 \stackrel{ }{\to }{\mathrm{H}}_2{\mathrm{NO}}_3^{+} + {\mathrm{HSO}}_4^{-} \\ \mathrm{base} \mathrm{acid} \\ {\mathrm{H}}_2{\mathrm{NO}}_3^{+} \stackrel{ }{\to } {\mathrm{NO}}_2^{+} + {\mathrm{H}}_2\mathrm{O} \\ \mathrm{nitronium} \mathrm{ion} \end{gathered}$$

Hence, in this reaction HNO₃ acts as a base and H₂SO₄ as an acid.

In the Friedel-Crafts alkylation reaction, benzene reacts with an alkyl halide like methyl chloride (CH₃Cl) in the presence of a Lewis acid catalyst (anhydrous AlCl₃) to form an alkylated product, toluene.

Benzene having any activating group i.e., OH, R etc., undergoes electrophilic substitution very easily as compared to benzene itself. Thus toluene (C₆H₅CH₃ ), phenol (C₆H₅OH) undergo electrophilic substitution very readily than benzene. Chlorine with +E and +M effect deactivates the ring due to strong -I effect. So, it is difficult to carry out the substitution in chlorobenzene than in benzene,so correct order is:-

Phenol>Toluene>Benzene>Chlorobenzene
(iv) (ii) (i) (iii)

 strong basic medium generally gives E 2 mechanism.

(d) All are covalent molecules. A covalent solid has atoms as constituent units at lattice points held together by covalent bonds.

(a) normal molar mass/exp. molar mass = 1+ $\mathrm{\alpha }$; (Molar mass = 2 x VD)

M1 =2*46=92

m2=2*24.5=49

                                                  92/49 = 1+ $\mathrm{\alpha }$

                                                .^.. $\mathrm{\alpha }$ =0.87