Final answer:
When changing from no grid to an 8:1 grid, the mAs must be increased by a factor of two.
Step-by-step explanation:
The correct answer is a. 2X. When changing from no grid to an 8:1 grid, the mAs (milliampere-seconds) must be increased by a factor of two. This is because using a grid reduces the amount of scatter radiation reaching the image receptor, which allows for a higher quality image. However, the grid also absorbs some of the primary radiation, so the mAs must be increased to maintain an appropriate exposure.