1. The problem statement, all variables and given/known data A gas bottle contains a mixture of Helium and Oxygen molecules (O2 is diatomic). The root-mean-square velocity for the O2 molecules is 482 m/s. Find vrms for the Helium atoms. 2. Relevant equations 1/2mv^2=1/2mv^2 and solve for velocity of He, however, i am not sure what numbers to plug in for the mass. 3. The attempt at a solution I filled everything in but the masses, I know that oxygen is diatomic, or O2, but what does that mean I put in for the mass? Do I need to use the mass numbers by looking at a periodic table?