Is an identity function one – one function?

If $f$ is a bijection from $A$ to $B$, then $n\left(A\right)=n\left(B\right)$.

If $n\left(A\right)=n\left(B\right)$, then $f$ is a bijection from $A$ to $B$.

Determine whether the graph given below represent a function. Give reason for your answer.

Determine whether the graph given below represents a function. Give reason for your answer.

Determine whether the graph given below represent functions. Give reason for your answers concerning each graph.

Determine whether the graph given below represent functions. Give reason for your answers concerning each graph.

Let $f: A\to B$ be a function defined by $f\left(x\right)=\frac{x}{2}-1,$ where $A=\{2,4,6,10,12\}, B=\{0,1,2,4,5,9\}.$ Represent $f$ by set of ordered pairs.