1. The problem statement, all variables and given/known data (introduction course of university physics) A 5.0- liter gas tank holds 1.7 moles of monatomic helium (He) and 1.10 mole of diatomic oxygen (O2), at a temperature of 260 K. The ATOMIC masses of helium and oxygen are 4.0 g/mol and 16.0 g/mol, respectively. What is the ratio of the root- mean- square (thermal) speed of helium to that of oxygen? Answer: C 2. Relevant equations V(rms) = sqrt(3kT/m) 3. The attempt at a solution This is the only equation I found from my book about rms speed of gas, but the variables seems unrelated at all. I have no idea on how to do it. Please tell me how to deal with it in a more detail way. Thank you very much.