Answer:
The the angle associated with the second dark fringe is 39.9°
Option (a) is correct.
Step-by-step explanation:
Given:
Wavelength of light
m
Width of the slit
m
Order of diffraction

From the formula of single slit diffraction,

Where
order of diffraction,
angle associated with second dark fringe.




39.9°
Therefore, the the angle associated with the second dark fringe is 39.9°