The speed of light in air is $3 \times 10^8 \, m/s$. What will be its speed in diamond,whose refractive index is $2.4$?

The apparent depth of water in a cylindrical water tank of diameter $2R \ cm$ is reducing at the rate of $x \ cm/minute$ when water is being drained out at a constant rate. The amount of water drained in $c.c./minute$ is: ($n_1 =$ refractive index of air,$n_2 =$ refractive index of water)

An insect starts moving up in a liquid from point $O$ with a variable refractive index $\mu = \mu_0(1 + ay)$,where $y$ is the depth of the liquid from the surface. If $u$ is the speed of the insect,what is its apparent speed to the observer $E$?

Light waves travel from an optically rarer medium to an optically denser medium. Its velocity decreases because of a change in . . . . . . .

When a light ray enters from medium $i$ to medium $j$,if $_i\mu_j$ represents the refractive index,what is the product of $_2\mu_1 \times _3\mu_2 \times _4\mu_3$?

When a light ray is incident on a medium at an angle $i$ and refracted into a second medium at an angle $r$,the graph of $\sin r$ vs $\sin i$ is as shown below. From this,one can conclude that:
$(A)$ Velocity of light in the second medium is $1.73$ times the velocity of light in the first medium
$(B)$ Velocity of light in the first medium is $1.73$ times the velocity in the second medium
$(C)$ The critical angle for the two media is given by,$\sin i_c = \frac{1}{\sqrt{3}}$
$(D)$ The critical angle for the two media is given by,$\sin i_c = \frac{1}{2}$