Answer :
When x-ray radiation and infrared radiation are
traveling in a vacuum, they have the same speed.
The correct answer is
(1) speed
In fact, the speed of an electromagnetic wave does not depend on the type of wave, but only on the medium: since both the waves are travelling in vacuum (same medium), they are travelling at same speed, which corresponds to the speed of light in vacuum:
[tex] c=3.0 \cdot 10^8 m/s [/tex]