(i) Null Set
(a) A = {x : x is a natural number less than 1}
(b) B = {x : x is a positive natural number which lies between 2 and 3}
(ii) Finite set
(a) A = {x : x2 < 10, where x is a prime number}
(b) B = {x : x, is any month of a year}
(iii) Infinite set
(a) P = {x : x = 2n, where n is a natural number}
(b) Q = {x : x = p/q, where p and q are integer and q ≠ 0}
(iv) Universal set
(a) Set of integers for natural numbers.
(b) Set of real numbers for natural numbers, integers and rational numbers.