The correct answer is option 1: Infrared rays.
In the electromagnetic spectrum, different types of waves are defined based on their wavelengths. Wavelength is the distance between two consecutive crests or troughs of a wave. The longer the wavelength, the lower the energy and frequency of the wave.
Infrared rays have the longest wavelength among the options given. This means that they have a larger distance between two consecutive crests or troughs compared to the other types of waves mentioned.
Gamma rays, on the other hand, have the shortest wavelength and therefore the highest energy and frequency. They have much smaller distances between crests or troughs compared to the other types of waves.
Light rays are a broad category and can have various wavelengths depending on whether they are in the visible spectrum or beyond. However, in general, they have shorter wavelengths than infrared rays.
Ultraviolet rays have shorter wavelengths than visible light but longer wavelengths than X-rays. Therefore, they have a shorter wavelength than infrared rays but longer than gamma rays.
Overall, the longest wavelength among the options given belongs to infrared rays.