First, every time when you ask question like this about function you must give elements of the initial set.
Definition of the function is - Every element of the starting set (domain- x)
must be related to only one element of the second set ( codomain-range-y).
In your case you have element (coordinate) x=3 which is in the relation with two elements (coordinates) y=2 and y=5 and that is relation but not function.
Good luck!!!
