Answer:
(C) increase the distance between the slits in the diffraction grating
Explanation:
This light always form constructive interference, the difference in distance is given λn.
where;
λ is the wavelength
n is the nth maxima
At center fringe, n = 0; the difference is 0
for the first maximum, n= 1, the difference is λ
for second maximum, n = 2, the difference is 2λ
for third maximum, n = 3, the difference is 3λ
From the above illustrations, the wavelength is constant, but the distances between the slits increases, resulting in a higher difference.
Therefore, Option C is the correct answer: increase the distance between the slits in the diffraction grating