The critical angle for diamond with respect to air is nearly (in $^{\circ}$)

If light travels a distance $x$ in $t_1 \, s$ in air and $10x$ distance in $t_2 \, s$ in a medium,the critical angle of the medium will be

In total internal reflection,when the angle of incidence is equal to the critical angle for the pair of media in contact,what will be the angle of refraction in degrees?

$A$ beam of light strikes a glass plate at an angle of incidence $60^{\circ}$ and the reflected light is completely polarized. The refractive index of the plate is:

Assertion $(A)$: Propagation of light through an optical fibre is due to total internal reflection taking place at the core-clad interface.
Reason $(R)$: Refractive index of the material of the core of the optical fibre is greater than that of air.

The phenomenon utilised in an optical fibre is