What is critical angle?

Explanation

The angle of incidence in the denser medium for which the angle of refraction in rarei- medium is `90^(@)`
When the angle of incidence in water reaches a certain critical value, the refracted ray lies along the boundary, having an angle of refraction of 90-degrees. This angle of incidence is known as the critical angle it is the largest angle of incidence for which refraction can still occur