If the x's repeat, then it is NOT a function.
For problem 2:
(3,5) and (6,5) actually don't cause a problem for us. Repeating y's in okay! So yes, this relation can be a function.
For problem 3:
(2,5) and (2,9) uh oh! We have x=2 being mapped to two different locations. Bad bad bad. This is NOT a function.