How can gravity overcome temperature and diffusion forces of gasses?

Gravity acts on gases as the molecules have mass. However, they are more influenced by temperature at our normal temperature range. At 25°C, the effect of temperature on molecular motion is about 30000 times higher than gravity forces. Thus, in gases, diffusion is more prominent compared to gravity.

considering the question as per the attachment

here we can see that the radon nuclide has 222 as the atomic mass number and 86 as the atomic number.

when it undergoes nuclear fission it gives polonium which has atomic mass number as 218 and atomic number will be 84 along with a helium nucleus which has 4 atomic mass number and 2 as its atomic number.

222 = 218 + 4 (atomic mass number)

86 = ? + 2; therefore ? = 86-2 = 84.

the atomic mass number of polonium will be 84.