(c)
Given, $f(n) = \left\{ \begin{array}{r}
\frac{n}{2},\ n\ is\ even \\
0,\ \ \ n\ \ is\ odd
\end{array} \right.\$
Here, we see that for every odd values of $z$, it will give zero. It means that it is a many one function.
For every even values of $z$, we will get a set of integers $( - \infty,\ \infty)$. So, it is onto. Hence, it is surjective but not injective.