Step 1: Angle of Deviation and Angle of Incidence
In a prism, the angle of deviation \( \delta \) varies with the angle of incidence \( i \). This relationship is important for understanding the refraction of light inside the prism. The deviation angle typically decreases with increasing incidence angle, reaching a minimum deviation \( \delta_{\text{min}} \), and then increases again.
The formula for the angle of deviation is given by:
\[
\delta = i + r - A
\]
Where:
- \( i \) is the angle of incidence,
- \( r \) is the angle of refraction inside the prism,
- \( A \) is the prism angle.
Step 2: Minimum Deviation
The graph shown in the image likely represents this behavior, where the angle of deviation is plotted against the angle of incidence. At the point of minimum deviation, the deviation is least, and the light ray passes symmetrically through the prism. The angle of incidence \( i_m \) at this point is known as the minimum angle of incidence.
Step 3: Conclusion
From the graph, the minimum deviation occurs when the angle of incidence \( i \) is at its lowest value, and from the given options, it is observed that this corresponds to:
\[
\boxed{(B)} \, 60^\circ
\]
