Light of Wavelength $\lambda$ Is Normally Incident on a Diffraction Grating G

Multiple Choice

Light of wavelength $\lambda$ is normally incident on a diffraction grating G. On the screen S, the central line is at P and the first order line is at Q, as shown. The distance between adjacent slits in the grating is:

A) 3 $\lambda$ /5
B) 3 $\lambda$ /4
C) 4 $\lambda$ /5
D) 5 $\lambda$ /4
E) 5 $\lambda$ /3