Electromagnetic Spectrum

As described in NCERT Class 12, Chapter 8 (Electromagnetic Waves), the electromagnetic spectrum arranges radiation in order of increasing frequency and decreasing wavelength: radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays. Radio waves occupy the low-frequency end with wavelengths ranging from a fraction of a metre up to several kilometres, the longest of all the listed bands. Since wavelength and frequency are inversely related through c = fλ, the lowest-frequency radio waves correspond to the greatest wavelengths, which is why they are ideal for long-distance broadcasting and communication. Gamma rays sit at the extreme high-frequency end and have the shortest wavelengths, so they are incorrect. X-rays also have very short wavelengths, well below a nanometre, and cannot be the answer. Ultraviolet rays have wavelengths shorter than visible light and thus far shorter than radio waves. A magnitude check confirms the ordering: kilometre-scale wavelengths clearly exceed the picometre wavelengths of gamma and X-rays, so radio waves are correctly chosen.