Final answer:
The function with a vertex on the y-axis is option B) fx) = x(x + 2).
Step-by-step explanation:
The function that has a vertex on the y-axis is option B.) fx) = x(x + 2).
To determine the vertex of a function, we need to look at the equation in the form of y = ax² + bx + c. In option B, we have y = x(x + 2) = x² + 2x, which matches the required form. Since b = 2, the vertex of the function is on the y-axis.