d
$\frac{{{{({V_{rms}})}_1}}}{{{{({v_{rms}})}_2}}} = \sqrt {\frac{{{T_1}}}{{{T_2}}}} $
$\Rightarrow$ $\frac{{500}}{{{{({v_{rms}})}_2}}} = \sqrt {\frac{{0 + 273}}{{819 + 273}}} = \sqrt {\frac{{273}}{{1092}}} $
${({v_{rms}})_2} = 500\sqrt {\frac{{1092}}{{273}}} $
$ = 500\sqrt 4 = 1000\frac{m}{{\sec }} = 1\frac{{km}}{{\sec }}$