Answer
The function is not a one-to-one function.
Work Step by Step
For a function to be one-to-one, for each value of $x$, there must be a unique $y$ value paired with it and every element of the domain (D) must be paired with a unique element of the range (R).
We can notice that that the domain elements John and Chuck are both paired with the same element of the range Phoebe.
Therefore, the function is not a one-to-one function.
