What of the following electromagnetic waves has the longest wavelength ?

The electromagnetic spectrum is organized by wavelength and frequency. According to the standard order from longest to shortest wavelength, the sequence is radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays [t7]. Among the provided options, infrared rays have the longest wavelength, typically ranging from 1 to 100 microns [t2]. Visible light (light rays) follows with a shorter range of approximately 400 to 700 nanometers [t1][t6]. Ultraviolet rays are even shorter, falling below the violet end of the visible spectrum [t6]. Gamma rays possess the shortest wavelengths and highest frequencies in the entire spectrum [t5][t6]. While radio waves are the longest overall [c1][t4], within the specific subset of infrared, gamma, light, and ultraviolet, infrared is the longest [t7].

Sources

1. [1] https://imagine.gsfc.nasa.gov/science/toolbox/emspectrum1.html
2. [2] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 20: Earths Atmosphere > Explanation: > p. 279