Which of the following types of electromagnetic radiation travels at…

The correct answer is Option (4) → All of these travel at the same speed

All electromagnetic waves travel through vacuum with the same speed \( c=3\times10^{8}\,\mathrm{m\,s^{-1}} \), independent of wavelength. The types differ only in wavelength and frequency.

Option (1) Radio waves — Incorrect. Radio waves have the longest wavelengths of the three, but their speed in vacuum is still \( c \).

Option (2) Visible light — Incorrect. The speed of light in vacuum is \( c \), the same value as for the other two.

Option (3) X-rays — Incorrect. X-rays have the highest frequency of the three, yet in vacuum they too travel at \( c \).

Option (4) All of these travel at the same speed — Correct. Radio waves, visible light and X-rays are all electromagnetic waves, so each travels through vacuum at \( c \).

NCERT (2026-27):
Nature of Electromagnetic Waves – “The velocity of electromagnetic waves in free space or vacuum is an important fundamental constant. It has been shown by experiments on electromagnetic waves of different wavelengths that this velocity is the same (independent of wavelength) to within a few metres per second, out of a value of 3×10⁸ m/s.”