which type of electromagnetic wave travels through space the slowest?

a) All EM waves travel at the same speed
b) radio waves
c) microwaves
d) ultraviolet
e) infrared

For a vacuum, (a) is correct.

For your purposes, A would be correct. However, there are signals that are used, such as the ULF frequencies used for communication with submarines that do not travel at the speed of light. These are very low RF frequencies, almost in the audio band and would travel at the speed of sound which would be a lot slower than anything is your answers, but they are still classed as EM waves.

answer is "a".

All electromagnetic waves travel through space at the same speed which is the speed of light approx equal to 300 000 Km/sec