Question

if the point $(x, y)$ is on the $y$-axis, which of the following must be true?
$x = 0$
$y = 0$

Explanation:

Points on the y-axis have an x-coordinate of 0, as the y-axis is defined as the line where the horizontal (x) value is 0. A y-coordinate of 0 describes points on the x-axis, not the y-axis.

Answer:

$x=0$