The correct answer is C:1
Expression of rms is, \(u_{rms}=\sqrt{\frac{3RT}{M}}\)
\(\Rightarrow \, \, \, \, \frac{u_{rms}(H_2\, at\, 50\, K)}{u_{rms}(O_2\, at\, 800\, K)}=\frac{\sqrt{\frac{3R\times50}{2}}}{\sqrt{\frac{3R\times800}{32}}}\)
\(\, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \sqrt{\frac{50}{2}\times\frac{32}{800}}=1\)