(i) Set of integers which lie between 2 and 3 .

This is set. We know that there is no that lie between 2 and 3.

(ii) Set of natural numbers that are smaller than 1.

This is also a set. We know that there is’ no number less than ‘1’.

(iii) Set of odd numbers that leave remainder zero, when divided by 2.

This is a set. We know that numbers do not leave remainder zero when divided by 2.