One-to-one function:

A function is one-to-one if any two different inputs in the domain correspond to two different outputs in the range.

If and are two different inputs of a function , then is one-to-one if .

Observe the domain and range of the function, the element Phoebe in the range is mapped with two different elements in the domain that is John and Chuck.

So the function is not a one to one function.

The function is not one to one function.