Solution :

Since the graph intersects the vertical line (y-axis) at two points, it is not a function.

Solution :

The given graph intersects the vertical line (y-axis) at one point. It is a function.

(iii)

Solution :

The graph intersects the y-axis at three points, hence it is not a function.

Solution :

The graph intersects the vertical line at most one point. Hence it is a function.