a
(a) \(\frac{{{\mu _2}}}{{{\mu _1}}} = \frac{{{v_1}}}{{{v_2}}} = \frac{1}{2} \Rightarrow \frac{{{\mu _1}}}{{{\mu _2}}} = 2({\mu _1} > {\mu _2})\)

For total internal reflection \(_2{\mu _1} = \frac{1}{{\sin C}} \Rightarrow \frac{{{\mu _1}}}{{{\mu _2}}}\)

\( = \frac{1}{{\sin C}} \Rightarrow 2 = \frac{1}{{\sin C}} \Rightarrow C = {30^o}\) So, for total (Internal reflection angle of incidence must be greater than \(30°.\)