Hi aspirant, If I say that AA is having all the elements which are in BB , which means that AA is a subset of BB , but AA is not equal to BB , then AA is known to be a proper subset of BB. If I say that AA is having all the elements which are in BB , and AA is equal to BB , then AA is an improper subset of BB .

The example of a set containing only one subset which should be an improper subset is the null subset.

Remember: Null set is known to be the empty set in Set Theory of Mathematics. It is the set that contains no elements.