Among given aliphatic amines, 2° amine is most basic, followed by 3° amine and 1° amine.
Therefore, the correct basic strength (Kb) order of the given amines is
(C) > (D) > (B) > (A)
The pKb order of the given amines will be just the opposite of their basic strength order.
The order is (A) > (B) > (D) > (C)
So the correct answer is A-III, B-IV, C-II, D-I