$A$ ray of light is incident on an equilateral glass prism placed on a horizontal table. For minimum deviation,which of the following is true?

When a glass prism of refracting angle $60^\circ$ is immersed in a liquid,its angle of minimum deviation is $30^\circ$. The critical angle of glass with respect to the liquid medium is......$^\circ$

We use a flint glass prism to disperse polychromatic light because light of different colours:

$A$ thin prism $P_1$ with an angle $6^{\circ}$ and made of glass of refractive index $1.54$ is combined with another prism $P_2$ made from glass of refractive index $1.72$ to produce dispersion without average deviation. The angle of prism $P_2$ is $........{}^{\circ}$

An achromatic prism is made by combining two prisms $P_1$ $(\mu_v = 1.523, \mu_r = 1.515)$ and $P_2$ $(\mu'_v = 1.666, \mu'_r = 1.650)$,where $\mu$ represents the refractive index. If the angle of the prism $P_1$ is $10^o$,then the angle of the prism $P_2$ will be.....$^o$

Derive the expression $\delta = i + e - A$ for a prism.