Explain when a relation is not a function?

Answer: Every domain element is paired with only one range element. No two pairs share the same domain element.

Solution:

A function is always a relation but a relation is not always a fucntion.

For example

we can make a realtion of student roll number and their marks obtained in mathematics.

So we can have pairs like (a, b), (c, d) ... etc.

Its a realtion but it may not be function. Because function follows that for same input there should not be diffrent output. But this doesn't holds a necessary condition in case of relation.

Because two diffrent students with two diffrent Roll number may have same marks.