A ray is incident at an angle of incidence on one surface of a prism of small-angle A and emerges normally from the opposite surface. If the refractive index of the material of the prism is $\mu$, the angle of incident i is nearly equal to:

Given data: 

the incidence's inclination =i

The prism's oblique angle =A

The direction of emergence =e

Refractive index of the prism's material is μ.

The angle of deviation, in the case of a small-angle prism $\delta =(\mu -1)\mathrm{A}$
Because the beam appears properly,

$\therefore \mathrm{e}=0$
the relationship,
$A+\delta =i+e$
We have, $\mathrm{i}=\mathrm{A}+\delta$
$\text{ or }\delta =(\mathrm{i}-\mathrm{A}) \dots \dots \dots ..\left(\mathrm{ii}\right)$
From Eqs. (i) and (ii)
$(\mathrm{i}-\mathrm{A})=(\mu -1)\mathrm{A}$
$\Rightarrow \mathrm{i}=\mu \mathrm{A}\text{. }$

Hence, the correct answer is option D.