Question

11. Reflecting telescopes are popular because they're _______ than a refracting telescope.

Answer 1

I do not know what the school expects as an answer, but advantage of reflecting telescopes is that there is only one major reflecting surface, so it is quite easy to create a 6 or 8 inch telescope by an amateur, after adding on a prism and an eyepiece.  (a microscope eyepiece could be used).
MY answer would be "easier to build".  (it still takes tens of hours to grind and polish the single plane surface to a parabolic surface).

Electromagnetic waves all have the same velocity in the same medium.  However, since frequencies vary widely, so do wavelengths.

Answer 2

for 11. the answer is they are D. easier to build. hope i helped (: