Explain the following percentages of meta electrophilic substitutions.
(a) `underset(4.4%)(C_(6)H_(5)CH_(3)),underset(15.5%)(C_(6)H_(5)CH_(2)CI),underset(33.8%)(C_(6)H_(5)CHCI_(2)),underset(64.6%)(C_(6)H_(5)C CI_(3))`
(b) `underset(100%)(C_(6)H_(5)N(CH_(3))_(3)),underset(88%)(C_(6)H_(5)CH_(2)N(CH_(3))_(3)),underset(19%)(C_(6)H_(5)CH_(2)overset(+)N(CH_(3))_(3))`

Explanation

(a) Successive replacement of hydrogen atoms in electron releasing group `(-CH_(3))` by electronegative chlorine atoms makes the group increasingly electron attracting and meta-directing.
(b) The +ve charge on N makes the substituent electron attreacting and meta-directing. The positive charge decreases succuessively by inserting electron releasing `-CH_(2)` groups and thus o-, p-orientation dominates in `C_(6)H_(5)CH_(2)CH_(2)overset(+)N(CH_(3))_(3).`