Answer
The rms speeds of different molecules are:
(e) inversely proportional to $\sqrt{molecular~mass}$
Work Step by Step
In an ideal gas, the average kinetic energy of the molecules is $\overline{KE} =
\frac{3}{2}kT$
Then:
$\frac{1}{2}m\overline{v^2} = \frac{3}{2}kT$
$v_{rms} = \sqrt{\frac{3kT}{m}}$
The rms speeds of different molecules are:
(e) inversely proportional to $\sqrt{molecular~mass}$
