A grayscale image is one in which each pixel can be white, or black, or various shades

Question:

A grayscale image is one in which each pixel can be white, or black, or various shades of gray in between. Assuming that there are 256 discernable shades of gray, how many bits would a bitmap require to represent a pixel in a grayscale image? How does this number compare to those for black-and-white and color bitmaps?