the questions says given vertices ABC which with the following vertices(4,8) b(1,5) and c (6,3) .which of the following are coordinates of the vertices of A'B'C after reflection across y=2 is applied?

Let's draw a diagram to represent the given situation.
The image below shows the triangle ABC and the line y = 2.
We just have to draw one symmetric triangle under the line y = 2.
Are you can observe in the image above, the vertices of the reflection are: A'(4, -4), B'(1, -1), and C'(6, 1).