A point source S is placed at the bottom of different layers as shown in the figure. The refractive index of bottom most layer is `mu_(0)`. The refractive index of any other upper layer is `mu(n)=mu_(0)-(mu_(0))/(4n-18)` where n=1,2………….A ray of light with angle i slightly more than `30^(@)` starts from the source S. Total internal reflection takes place at the upper surface of a layer having n equal to

Options

A. 3
B. 5
C. 4
D. 6

Answer

C