Question

What is critical angle for water air medium if the refractive index

Answer 1

I think your question is incomplete

Answer 2

When a ray of light travels from a optically denser medium to an optically rarer medium, there is an angle of incidence in the denser medium for which the angle of refraction in the rarer medium is 90°. This angle of incidence is known as critical angle for a given pair of media.