Question

A ray of light is incident at the glass water interface at an angle i ,it emerges finally parallel to the surface of water ,then the value of refractive index index of glass will be?

Answer 1

the ray of light enters from glass medium into water medium at angle of incidence = i.    Ray emerges parallel to the surface of water... Angle of refraction = 90 deg.  Also we can deduce that glass is optically denser than water.

 so "i" = critical angle of the glass-water interface....
   
$sin\ i = \frac{\mu_{water}}{\mu_{glass}}\\\\\mu_{glass}=\frac{4}{3}\frac{1}{sin\ i}$