Define null set, give example.

Hint: In this question it is given that we have to define null sets with example. So for this first we have to know about null sets, or what is a null set and why we call it a null set.

Complete step-by-step answer:
Definition: If a set does not contain any element or member then the set is called a null set. Null set is also called a void set or empty set. The symbol used to represent an empty set is – $\phi$ ,{}.

Examples:
1) Let A = {x :1 < x < 2, x is an integer } be a null set because there is no integer between numbers 1 and 2. Therefore, A = {} or $\phi$
2) Let W = {d: d > 8, d is the number of days in a week} will also be a void set because there are only 7 days in a week.

Note: Always remember that a null set implies no elements in a set but here it does not mean that the element is zero.i.e, {0}, because if you write {0} then it is not a null set , since this set has an element which is zero.