Order of a set : There is no restriction on the number of members of a set . A set may have 0,1,2,3,4 or any number of elements. sets with zero or one element deserve special attention. According to the every day use of the word set or collection it must have at least two elements. But in mathematics it is found convenient and useful to consider sets which have only one element or no element at all.

Singleton set: A set having only one element is called a singleton set.

Example: 1

{5}, {6},{ 1} here order of set is one

Empty sets or null set: A set having no elements ( zero number of elements) is called the empty set or null set. the empty set is denoted by the symbol Φ or { }. Order of set is zero or no element in the set.

Example: 2

The set of odd integers between 2 and 4 is a singleton that is the set {3}. here order of set is one. and the set of even integers between the same numbers is the empty set.empty set is denoted by the symbol Φ or { }. here order of set is zero.

Singleton set having zero Element:

The set {0} is a singleton set having zero as its element, this type of set is not empty set.