Assertion: Critical angle of light passing from glass to air is minimum for violet colour.

Reason: The wavelength of violet light is greater than the light of other colours.

Assertion: A concave mirror of some focal length in air is used in a medium of refractive index $2.$ Then the focal length of the mirror in that medium will remain the same.

Reason: The focal length of a mirror is half of the radius of curvature of the mirror.

Assertion: We cannot produce a real image by plane or convex mirrors under any circumstances.

Reason: The focal length of a convex mirror is always taken as positive.

Assertion: The frequencies of incident, reflected and refracted beam of monochromatic light incident from one medium to another are same.

Reason: The incident, reflected and refracted rays are coplanar.

Assertion: A convex lens of glass $({\mu }_2=1.5)$ behave as a diverging lens when immersed in carbon disulphide of higher refractive index $({\mu }_1=1.65)$.

Reason: A convex lens is thinner in the middle and thicker at the edges.

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.