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	$2.42$

(N/A) The optical density of a medium is directly related to its refractive index. $A$ medium with a higher refractive index has a higher optical density,and a medium with a lower refractive index has a lower optical density.
$1$. Highest optical density: By comparing the refractive indices in the table,Diamond has the highest refractive index of $2.42$. Therefore,Diamond has the highest optical density.
$2$. Lowest optical density: By comparing the refractive indices in the table,Air has the lowest refractive index of $1.0003$. Therefore,Air has the lowest optical density.