Light travels in a straight line because :
(A) it is not absorbed by atmosphere
(B) its velocity is very high
(C) diffraction effect is negligible
(D) due to interference

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Hint: Light travels in a straight line because the diffraction effect is least due to the small wavelength of light. So the small wavelength of light produces negligible diffraction and therefore light travels along a straight line.

Complete step by step answer:
A) light is not absorbed by atmosphere: this option is incorrect as light is absorbed by air and particles present in the atmosphere scatters light and redistributes any light energy in the atmosphere, therefore is not responsible for light to travel in a straight line.
B) its velocity is very high: this option is incorrect as although it is a fact that light has a very high velocity,this plays no role in the straight line path of light.
C) diffraction effect is negligible: this option is correct as light has a very small wavelength and therefore gets diffracted negligibly resulting in straight line motion of light.
D) due to interference: this option is incorrect as interference is the intersection of two or more light waves due to the straight line motion of light and therefore it is a consequence of straight line motion of light.

Hence,option (C) is the correct answer.

Note: When light passes through a small opening, comparable in size to the wavelength λ of the light, the wavefront on the other side of the opening resembles the wave. Let us know more about the diffraction of light and single slit diffraction that occurs when light travels through a single slit.
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