(a)\\\\(\\mu_1=1.68,\\mu_2=1.44\\\\)\\\\(\\mu_1/\\mu_2=1/sini_1\\Rightarrow i_1=59^o\\\\)For critical angle, total internal reflection takes place when \\\\(i \\gt i_1\\\\)maximum angle of reflection is \\\\(90-i_1=31^o=r_{max}\\\\)Let \\\\(i_{max}\\\\) be the maximum angle of incidence.\\\\(\\mu_1=sini_{max}/sinr_{max}\\Rightarrow i_{max}=60^o\\\\)Thus all the ray between \\\\(0^o\\lt i\\lt60^o\\\\) will suffer TIR.(b)Now, \\\\(\\mu_1=1\\\\) (air)\\\\(sini/sinr=\\mu_2/\\mu_1\\Rightarrow r=36.5^o\\\\)\\\\(i=90-36.5=53.5^o\\\\)Since \\\\(i\\gt r\\\\), all incident ray will suffer TIR