Pick out the longest wavelength from the following types of radiation. 

Wavelength of red light is longest.

wavelength Range of :

blue light:  $4.5\times {10}^{-7}-4.85\times {10}^{-7} m$

Gamma : $< {10}^{-12} m$

X-rays:  ${10}^{-9} m – {10}^{-12} m$

red light : $6.25\times {10}^{-7}–7.5\times {10}^{-7} m$