1. For a prism, the angle of deviation is

where:

• $i$ = angle of incidence
• $e$ = angle of emergence
• $A$ = prism angle

2. As the angle of incidence $i$ changes, the deviation $\delta$ does not change linearly.

3. Important property of a prism:

• The deviation first decreases with increase in $i$
• It reaches a minimum value $\delta_{\min}$
• Then it increases again

So the graph of $\delta$ vs $i$ is a U-shaped curve.

4. At minimum deviation condition:

and the path of the ray inside the prism is symmetric.

5. Therefore, the correct graph is the one that shows:

• decreasing deviation initially,
• then a minimum,
• then increasing deviation.

Hence, the correct option is C.