The first group have 2 ordered pairs (0, 1) and (0, 5) in which there are 2 values of y linked to one value of x, which makes it a relation but not a function.
In the second group each value of x is linked to one and only one value of y which makes it a function.
A function is either a one-to-one ( like the second group) or a many-to-one relation.
A one-to-many relation as exists in the first group is a relation but it's not a function.
