A light with a second-order dark band forms a diffraction angle of 20.0 degrees. The diffraction grating has 200.0 lines per mm. The wavelength of the light, to the nearest whole number, is nm.

The value is

Explanation:

From the question we are told that

     The order of the dark fringe is  m  =  2

      The diffraction angle is  

       The diffraction grating is  

Generally separation between the slits is mathematically represented as

=>      

Generally the condition for destructive interference is mathematically represented as

=>    

=>  

=>