Question

What is the critical angle for light traveling from water (n=1.333) into ice (n=1.309)?

Answer 1

The critical angle is the angle of incident in the optically dense media that produces the angle of refraction as 90°.

sin c =1/n, where n is the refractive index and c is the critical angle. 
Also, n1sinФ1=n2sinФ2

In this case we have,
1.33×sinc = 1.309×sin90°     Where c is the critical angle. 

sin c =1.309/1.33

sin c = 0.981995498

      c = 79.11°