Answer: The correct option is
(A) The sign of the x-coordinate changes; the y-coordinate stays the same.
Step-by-step explanation: We are given to describe the change that occurs to the coordinates of a vertex of a figure when it is reflected across the y-axis.
We know that
if a point (x, y) is reflected the Y-axis, then its x co-ordinate will change sign. The y co-ordinate remains the same.
That is,
After reflection across the Y-axis, the co-ordinates (x, y) changes to (-x, y).
For example, the point (4, 2) and its reflection across the Y-axis is shown in the attached figure below. Its image after the reflection is (-4, 2).
Therefore, the correct description is
The sign of the x-coordinate changes; the y-coordinate stays the same.
Thus, (A) is the correct option.