If a function is defined as $f:\mathbb{N}\to \mathbb{N},f(x)=\frac{x-1}{2}$, then which of the following is true regarding this function?

A function $f:A\to B$ must assign an element of $B$ to every element of $A$.The domain is $\mathbb{N}=\{1,2,3,\dots \}$.For $x=1$, $f(1)=\frac{1-1}{2}=0$.However, $0\notin \mathbb{N}$ (the codomain). Since an element of the domain does not have a valid image in the codomain, $f$ is not a validly defined function on these sets. Thus, the data is incorrect/invalid.