$(a)$ 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.

(N/A) Alcohol is optically denser than water. This is because a higher refractive index indicates a higher optical density.
The ray diagram shows light bending towards the normal when passing from a rarer medium (water) to a denser medium (alcohol).
$(b)$ Given:
Absolute refractive index of diamond,$n_d = 2.42$
Absolute refractive index of glass,$n_g = 1.50$
Refractive index of diamond with respect to glass,$_g n_d = \frac{n_d}{n_g}$
$_g n_d = \frac{2.42}{1.50} = 1.6133$ (approximately $1.61$)