The path of a ray of light coming from air passing through a rectangular glass slab traced by four students are shown as $A, B, C$ and $D$ in the figure. Which one of them is correct?

$A$ ray of light is incident obliquely on a glass slab. Draw a ray diagram showing the path of the light ray. Clearly,mark the angle of incidence,angle of refraction,angle of emergence,and lateral displacement of the ray. Give a formula to find the refractive index of the glass slab in terms of the angle of incidence and the angle of refraction.

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.

Which of the following has the minimum 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	$2.42$

$(a)$ Water has a refractive index of $1.33$ and alcohol has a refractive index of $1.36$. Which of the two media is optically denser? Give a reason for your answer. Draw a ray diagram to show the path of a ray of light passing obliquely from water to alcohol.
$(b)$ The absolute refractive index of diamond is $2.42$ and the absolute refractive index of glass is $1.50$. Find the refractive index of diamond with respect to glass.