Twinkling of stars is due to?

Science Behind Star Light 

• The environment is constantly changing (due to which the optical densities of air at different levels in the atmosphere keep on changing).
• Due to atmospheric refraction, the starlight that reaches our eyes fluctuates constantly.
• And at night, it seems that the star is twinkling.

When light strikes a smooth surface, reflection occurs when the light bounces off the surface. The phenomenon of scattering of light occurs when light beams deviate from their intended route after colliding with an obstruction like dust, gas molecules, water vapours, etc. All of the light is reflected back into the first medium when the incidence angle is larger than the critical angle. Total internal introspection is the ailment.

Summary:

Twinkling of stars is due to? (A) Atmospheric reflection (B) Scattering of light (C) Internal reflection (D) Atmospheric refraction

The reason stars twinkle is because of atmospheric refraction. Because of the different optical densities of air at varying altitudes, when light from star enters the atmosphere of earth, it gets refracted.