Question

$\left(I\right)Chlorobenzene$ $\left(II\right)2,4-dinitrochlorobenzene$ $\left(III\right)p-nitrochlorobenzene$

The decreasing order of their reactivities towards electrophilic substitution reaction is:

• A. $\left(I\right)>\left(II\right)>\left(III\right)$
• B. $\left(I\right)>\left(III\right)>\left(II\right)$
• C. $\left(II\right)>\left(I\right)>\left(III\right)$
• D. $\left(III\right)>\left(I\right)>\left(II\right)$

Answer 1

The correct option is B $\left(I\right)>\left(III\right)>\left(II\right)$

The above given compounds are all benzene derivatives,
Electrophilic substitution reaction depends on the electron density of the ring and substituents present on the ring.
More the Electron withdrawing groups (deactivating groups) on the ring less reactive it is towards electrophilic substitution.
In Chlorobenzene $Cl$ is the only deactivating group present, whereas for $p-nitrochlorobenzene$ there are two deactivating groups present and in $2,4-dinitrochlorobenzene$ there are three deactivating groups present so it undergoes electrophilic substitution reactions with lesser rate when compared with I & III.
Thus, the rate of electrophilic substitution reaction is:
$I>III>II$