What are the units of refractive index?

Find out,from the table,the medium having the highest optical density. Also,find the medium with the lowest optical density.

Material medium	Refractive index
Air	$1.0003$
Ice	$1.31$
Water	$1.33$
Alcohol	$1.36$
Kerosene	$1.44$
Fused quartz	$1.46$
Turpentine oil	$1.47$
Benzene	$1.50$
Crown glass	$1.52$
Canada Balsam	$1.53$
Rock salt	$1.54$
Carbon disulphide	$1.63$
Dense flint glass	$1.65$
Ruby	$1.71$
Sapphire	$1.77$
Diamond	$2.42$

$(a)$ State the laws of refraction.
$(b)$ $A$ ray of light enters from a medium $A$ into a slab made up of a transparent substance $B$ (as shown in the figure). The refractive indices of medium $A$ and $B$ are $2.42$ and $1.65$ respectively. Complete the path of the ray of light until it emerges out of the slab.

What happens when a light ray incident normally on the surface of a glass slab enters from air into the glass?

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

How is the refractive index of a medium related to the speed of light? Obtain an expression for the refractive index of a medium with respect to another in terms of the speed of light in these two media.