Which symbol is used for the refractive index?

What is the ratio of the velocity of light in a transparent medium with a refractive index of $1.5$ to the velocity of light in a vacuum?

$(a)$ For the same angle of incidence $45^{\circ}$,the angle of refraction in two transparent media $I$ and $II$ is $20^{\circ}$ and $30^{\circ}$ respectively. Out of $I$ and $II$,which medium is optically denser and why?
$(b)$ Light enters from air to diamond,which has a refractive index of $2.42$. Calculate the speed of light in diamond,if the speed of light in air is $3.00 \times 10^{8} \text{ m s}^{-1}$.

You are given kerosene,turpentine,and water. In which of these does the light travel fastest? Use the information given in the table below.

Material medium	Refractive index
Water	$1.33$
Kerosene	$1.44$
Turpentine oil	$1.47$

What is meant by a lateral shift?

On what factor does the lateral shift produced by a glass slab depend?