Which statement is true about the speed of waves in the electromagnetic spectrum?

a) the speed of all electromagnetic wave is inversely proportional to their wavelength.
b) the speed of all electromagnetic waves is directly proportional to their frequency.
c) in a vacuum, all electromagnetic waves travel at speeds between 1.098 x10^5 and 2.998 x 10^8 m/s.
d) in a vacuum, all electromagnetic waves travel at the peed of 2.998 x 10^8 m/s.

d) in a vacuum, all electromagnetic waves travel at the peed of 2.998 x 10^8 m/s.

Explanation:

Electromagnetic waves are transverse waves produced by the oscillations of electric field and magnetic field. These waves, contrary to mechanical waves, do not need a medium to propagate, so they can also travel through a vacuum and empty space.

Moreover, all electromagnetic waves (regardless of their frequency or wavelength) travel at the same speed in a vacuum, and the value of this speed is called "speed of light":

This value becomes smaller when an electromagnetic wave travels through a medium.

gas and liquid