The polarizing angle in air for diamond is 67.4°. calculate the critical angle inside the diamond for total internal reflection.

Polarizing angle, also known as Brewster's angle, is the angle at which light should be incident for reflection not to take place.
It is given by;

Polarizing angle = tan^-1 (n2/n1), where n2 = index of diamond, n1 = index of air (= 1)

Sunstituding
67.4 = tan^-1(n2/n1) => tan 67.4 = n2/1 => n2 = tan 67.4 = 2.4023

If the light moves in the opposite direction;
Sin (critical angle) = n1/n2 = 1/2.4023 = 0.4163
Critical angle = Sin^-1(0.4163) = 24.60°