Light is incident from water onto a flat transparent slab of material, at an angle of 48.8° with the normal. The reflected ray and the refracted ray are perpendicular to each other.

Question

What is the index of refraction of the transparent substance?

Answer 1

The index of water is 1.33.

That happens to be the Brewster angle in this case, since the reflected and refracted rays are perendicular.

tan48.8 = n2/n1 = n2/1.33
n2 = 1.52

http://webphysics.davidson.edu/physlet_resources/bu_semester2/c27_brewster.html