Chemistry - Ideal Gas Question with Solution | TestHub

With $n\ge 2$ the series starts at $C_2{H}_2$, so the second member is $C_3{H}_4,M=40$.

$u_{mp}=\sqrt{2RT/M}$ and $u_{rms}=\sqrt{3RT/M}$.

Set $2T/40=3\times 400/32=37.5$, so $T=750$ K.

$T=750-273=477^{\circ }C$.

750 is the value in kelvin.

Answer: (B).