Answer
Not one-to-one.
Work Step by Step
A function is one-to-one if different inputs have different function values.
Algebraically written, $x_{1}\neq x_{2}\Rightarrow f(x_{1})\neq f(x_{2})$
Here we can find a pair of x-values from the domain of f for which this is not true.
For instance, $-1\neq 1,$ but
$f(-1)=(-1)^{2}+3=4$
$f(1)=1^{2}+3=4$.
Not one-to-one.
