A Helium-Neon Laser $\lambda$ = 6328 Nm) Is Used to Calibrate a Diffraction Grating

Multiple Choice

A helium-neon laser ( $\lambda$ = 632.8 nm) is used to calibrate a diffraction grating.If the first-order maximum occurs at 20.5 $\degree$ , what is the line spacing, d?

A) 1.81* 10-6 m
B) 1.00* 10-5 m
C) 1.00 * 10-4 m
D) 1.31 * 10-6 m
E) 6.76 * 10-7 m