\({\mu _1} + {\mu _2} = \mu _1' + \mu _2'\)
\(\frac{{PV}}{{R(273)}} + \frac{{PV}}{{R(273)}} = \frac{{1.5\,PV}}{{R(273)}} + \frac{{1.5PV}}{{R(T)}}\)
\(\Rightarrow\) \(\frac{2}{{273}} = \frac{{1.5}}{{273}} + \frac{{1.5}}{T}\)
\(\Rightarrow\) \(T = 819\,K = 546^\circ C\)