Question

why an empty set is called a set,when a set is a collection of elements?

Answer 1

An empty set is not nothing.Instead it is a set with no elements.

Just think of a bottle in which we used to put water .If there is no water in the bottle , we used to call it an empty bottle.
In the same way ,if there is no elements in a set,we used to call it an empty set as it is still representing a set having zero number of elements