Concept:The electromagnetic spectrum arranges radiations by wavelength, from longest to shortest.
Explanation:Radio waves lie at the low-frequency end of the electromagnetic spectrum.
They have very large wavelengths compared to infrared rays, X-rays, and gamma rays.
The order from longest wavelength to shortest is: radio waves, infrared, X-rays, gamma rays.
Therefore, among the given options, radio waves have the longest wavelength.
Answer:B. Radio wave