The clear sky looks blue because

The correct answer is D. dispersion of light.

When sunlight reaches the Earth’s atmosphere, it is scattered in all directions by all the gases and particles in the air. Blue light is scattered more than the other colors because it travels as shorter, smaller waves. This is why we see a blue sky most of the time.

Reflection is the bouncing of light off a surface. Refraction is the bending of light as it passes from one medium to another. Diffraction is the bending of light as it passes through a narrow opening or around an object.

The other options are incorrect because they do not explain why the sky looks blue.