Can you help me with this problem on root square mean?

Question

According to kinetic-molecular theory, in which of the following gases will the root square mean speed of the molecules be the highest at 200°C?

 

A. SF6

 

B. H2O

 

C. Cl2

 

D. HCl

 

E. None

Answer 1

At the same temperature, the kinetic energy of the gases is the same.  Therefore, the molecules of the gas of lowest molecular weight will have the highest v_rms.  Find and compare the molecular weights of the gases in the list, and select the one with the lowest molecular weight.  At a given temperature, that is the one whose molecules will move the fastest.