A
Angle at which light travels along the boundary between two media
B
Angle at which refraction stops
C
Angle at which a lens focuses parallel rays
D
Angle of maximum diffraction
Correct Answer: Option A — Angle at which light travels along the boundary between two media
Explanation:
The critical angle is the angle of incidence in the denser medium at which the refracted ray travels along the boundary and above which total internal reflection occurs.