Which molecule has the greatest average velocity at 100 degrees celsius.

He, Cl2, Xe, O2, NO2

I used the root mean squared formula but I think I did it wrong. I got Xe as my answer. Is this correct?

5 answers

From u = sqrt(3RT/M), the largest M will give you the smallest u. The smallest M will give you the largest u.
What is RT?

So for He I would do square root 3 times (value of RT) / 1.0079 correct?
R is 8.314
T is temperature.
However, you are asked only for the greatest, not a value. You don't need R or T.
so I just have to compare the molar mass of each gas and the smallest is the greatest?
Yes, if the root mean squared velocity is what you are looking for.