Twinkling of stars is due to:

We should have studied the idea of atmospheric refraction in order to answer this issue. When light or other electromagnetic waves travel through the atmosphere, they deviate from a straight line as a result of the changing air density as a function of altitude. This phenomenon is known as atmospheric refraction.

The refraction of starlight by the atmosphere is what causes the stars to twinkle. Atmospheric refraction is the term used to describe the refraction of light due to the earth's atmosphere having air layers with different optical densities.
The density of the air in the various levels of the atmosphere changes continually as a result of the physical characteristics of the atmosphere.
As a result, the different layers of the atmosphere's refractive index are constantly changing. Since starlight is subject to many refractions and changes in how much of it reaches the eye, it seems as though stars are twinkling as a result of this fluctuation in perceived brightness.

Hence, the correct answer is option B.