Answer : The incorrect option is, (b) they can travel at various speeds through any one material.
Explanation :
Electromagnetic waves : It is a type of energy which is produced by the oscillating magnetic and electric filed disturbance. Or we can say that it is produced by the movement of electric charged particles through the vacuum or matter.
It is a wave where the two vectors are vibrating mutually perpendicular to each other and in direction of the wave. The two vectors are electric field and magnetic field.
The gamma-rays, x-rays, ultraviolet-rays, infrared-rays, microwaves and radio-waves are the electromagnetic waves.
The characteristic of electromagnetic waves are :
- They can travel through the vacuum.
- They can travel through the matter.
- They can travel at same speeds through any of the material. That means the speed of light is always constant that is,

- They can be refracted.
- They can be reflected.
Hence, the incorrect option is, (b) they can travel at various speeds through any one material.