Arrange the following :
(a) In decreasing order of `p K_b` values
(I) `C_2H_5 NH_2`
(II) `PhNHMe`
(III) `(C_2H_5)_2 NH`
(IV) `PhNH_2`
(b) In increasing order of basic strength
(I) `PhNH_2`
(II) `PhNM_(e_2)`
(III) `(C_2H_5)_2 NH`
(IV) `MeNH_2`
( c)Increasing order of basic strngth (I) `PhNH_2`
(II) `p-`Nitroaniline
(III) `p-`Toluidine
(d) (I) `PhNH_2`
(II) `PhNHMe`
(III) `PhCH_2NH_2`
( e) In decreasing order of basic strength in gas phase.
(I) `C_2H_5 NH_2`
(II) `(C_2H_5)_2NH`
(III) `(C_2H_5)_3N`
(IV) `NH_3`.

Explanation

(a) `IV lt II lt I lt III` (aromatic amine `lt EDG, -Me` increases basicity `lt 1^@` amine `lt 2^@` amine)
(b) `I lt II lt IV lt III` (aromatic amine `ltEDG, -2 Me` increases basicity `lt 1^@` amine `lt 2^@` amine)
( c) `II lt I lt III (EWG, -NO_2`, decreases and `EDG, -CH_3`, increase basicity)
(d) `I lt II lt II` (aromatic amine `lt EDG, -Me` increases basicity ltbenzylamine, aliphatic amine).
( e) `III gt II gt I gt NH_3 (3^@ gt 2^@ gt 1^@ gt NH_3`, in gas phase).