What circles have their centers on the y-axis?

Answer 1

the ones that have

the point in the y axis

Answer 2

The circles that have their centers on the y-axis are those that have the equation x^2 + (y-k)^2 = r^2, where k is the y-coordinate of the center of the circle and r is the radius of the circle. In this case, the x-coordinate of the center is 0 since it lies on the y-axis.