Correct Answer - D
When total internal reflection just take place from lateral surface `i=C` i.e., `60^(@)=C`
`implies sin 60^(@)=sin C=(1)/(mu)impliesmu=(2)/(sqrt(3))`
Time taken by light to traverse some distance in a medium `t=(mu x)/(c)=((2)/(sqrt(3))xx10^(3))/(3xx10^(8))=3.85mu sec.`