Answer
Not one-to-one
Work Step by Step
To know if the given function represents a one-to-one function, perform the Horizontal Line Test.
If each horizontal line will pass through exactly one point of the graph, then the function is one-to-one.
Note that not all horizontal lines will intersect the given graph at exactly one point only (the green line intersects the graph in $3$ points).
This means that the given function is not an one-to-one function.