A diffraction grating has 400 lines per mm\text{mm}mm. When monochromatic light is incident normally on the grating, the second-order spectral line is formed at an angle of 30∘ 30^\circ\,30∘ from the normal to the grating.
What is the wavelength of the monochromatic light?
310 nm310\text{ nm}310 nm
420 nm420\text{ nm}420 nm
630 nm630\text{ nm}630 nm
1250 nm1250\text{ nm}1250 nm
