Speed of blue light in vacuum?

Q. State giving reason how the speed of red light is compared with the speed of blue light in vacuum and in glass.

Q. What is speed of light in vacuum? How does vacuum, force and air effects speed of light?

Q. Speed of light in vacuum is $km{s}^{-1}$

Q. The wavelengths for the light of red and blue colours are roughly $7.8\times {10}^{-7}m$ and $4.8\times {10}^{-7}m$ respectively. Which colour has the greater speed in vacuum?