average molecular velocity

The molecular velocity is inversely proportional to the square root of the mass of the particle -- net-net, the lightest particles move fastest -- make sense? Fortunately, since they are all being considered at once, you can estimate without taking the square root: just compare the molecular (or in one case atomic) mass:

H2O = 18.02 g/mole
He = 4.00 g/mole
HCl = 36.46 g/mole
BrF = 98.90 g/mole
NO2 = 46.00 g/mole

So in increasing order, you have BrF < NO2 < HCl < H2O < He

Hope that helped!