Answer: The sign of the x-coordinate changes.
Step-by-step explanation: Imagine the x-axis and y-axis, the x-axis account for how far over the point is and the y-axis is how high or low a point is. When reflecting across the y-axis, the height of the points are the same, but the positon of the points move left or right. Example: (3,5) when reflected across the y-axis becomes (3,-5).
Using basic terms here!
Hope this helps on your test/quiz!