Question

for all the functions of the form f(x) = ac^2 + bx + c, which is true when b=0

Answer 1

You didn't show us the choices.
The graph of that function would be centered on the y-axis.

Answer 2

These are the Choices:

The graph will always have zero x-intercepts.

The function will always have a minimum.

The y-intercept will always be the vertex.  

The axis of symmetry will always be positive.