Assertion: The twinkling of stars is due to the refraction of light.

Reason: The velocity of light changes while going from one medium to the other.

Assertion: The diamond shines due to multiple total internal reflections.

Reason: The critical angle for diamond is $24.4°$.

Assertion: There is no dispersion of light refracted through a rectangular glass slab.

Reason: Dispersion of light is the phenomenon of splitting of a beam of white light into its constituent colours.

Assertion: The blue colour of the sky is on account of the scattering of sunlight.

Reason: If the size of scatterer particles is very much smaller than the wavelength $(a<<\lambda )$ then, The intensity of scattered light varies inversely as the fourth power of wavelength of light.

Assertion : The Sun looks reddish at the time of sunrise and sunset because of scattering of light.

Reason : The wavelength of red colour is more than the wavelength of blue colour.

Assertion : A secondary rainbow have inverted colours than the primary rainbow.

Reason : The secondary rainbow is formed by single total internal reflection.

Assertion :If there had been one eye of the man then image would have not been seen three-dimensional and visible region would have decreased

Reason : By two eyes, we get two images of an object simultaneously from two different angles. Their superposition gives us the complete information about length, width and depth of the object.