what do you mean by an empty relation.pla tell me with the example. thnx

Empty Relation means the relation which does not have any element.

Suppose we were to define the relation R "sister of"  on the set of  boys school then it turns out to be a empty relation.

Again in terms of numbers

Consider the set A={1,2,3} B = {2,6,8}

Now if R is the relation square of from A to B

then R  is a empty relation