Which of the following statements is true?

According to the Cartesian sign convention in ray optics,

$A$ glass slab consists of thin uniform layers of progressively decreasing refractive indices $(RI)$ such that the $RI$ of any layer is $\mu - m \Delta \mu$. Here,$\mu$ and $\Delta \mu$ denote the $RI$ of the $0^{\text{th}}$ layer and the difference in $RI$ between any two consecutive layers,respectively. The integer $m = 0, 1, 2, 3, \ldots$ denotes the number of the successive layers. $A$ ray of light from the $0^{\text{th}}$ layer enters the $1^{\text{st}}$ layer at an angle of incidence of $30^{\circ}$. After undergoing the $m^{\text{th}}$ refraction,the ray emerges parallel to the interface. If $\mu = 1.5$ and $\Delta \mu = 0.015$,the value of $m$ is:

The distance travelled by light in glass (refractive index $= 1.5$) in a nanosecond will be.......$cm$.

The speed of light in a medium is $200 \times 10^8 \text{ cm/s}$. The refractive index of the medium is . . . . . . $(c = 3 \times 10^8 \text{ m/s})$.

When a light ray enters from air into water, which of the following properties does not change?