Final answer:
The coordinates of the reflected point B' across the x-axis are B'(0, 5), as it retains its x-coordinate and the y-coordinate changes sign.
Step-by-step explanation:
To find the coordinates of the reflection of point B across the x-axis, we simply need to change the sign of the y-coordinate while keeping the x and z-coordinates unchanged. Since point B is given as (0, -5) before the reflection, after reflecting point B across the x-axis, its new coordinates will be B'(0, 5). The z-coordinate is not provided, therefore, it is assumed that the reflection is in 2D space.