Answer: Hello mate!
f is something that assigns each student with a unique ID number.
We know that the relation between two quantities can be represented with a function, only when each point in the domain has a unique point in the codomain associated.
This means that for every point X in the domain, if f(X) = Y1, and f(X) = Y2, f only is a function when Y1 = Y2
Now, the students are the domain (X ) in this situation, and the ID numbers are the range or codomain (Y ), and we know that each student has a unique ID number, this means that each student has only one ID number, then when you evaluate the function with a student X, there is only one ID number Y that the function could assign him to, then this is a function.
