Two or more atoms join together to form a ?

gamma rays  < X-ray  < ultraviolet ray < visible light < infrared  < radio wave

Explanation:

given light form,

A) radio waves,B) infrared,C) visible light,D) ultraviolet,E) X-rays,F) gamma rays

we know,

wavelength of radio wave = 10000 Km

wavelength of infrared = 700 nanometers (nm) to 1 millimeter (mm)

wavelength of visible light = 380 to 740 nm

wavelength of ultraviolet ray = 10 nm to 400 nm

wavelength of X-ray =  0.01 to 10 nm

wavelength of gamma rays = 100 picometer

so, the order of rays.

gamma rays  < X-ray  < ultraviolet ray < visible light < infrared  < radio wave