Correct choice is (c) \(\frac {T_2}{T_1}\)=1
For explanation: A Mach wave is a normal shock wave of diminishing strength. It occurs for M=1 upstream. Then downstream M=1 also. And all the ratios are equal to 1, i.e \(\frac {P_2}{P_1}\)=1, \(\frac {T_2}{T_1}\)=1, \(\frac {\rho_2}{\rho_1}\)=1. This can be found by calculation when we put m=1. The properties across Mach wave do not change.