What has research determined about the orbit of an electron around a nucleus? Electrons orbit in exact energy levels. Electrons orbit the nucleus in circular motions exactly as shown on the classic Bohr model. Each sub-level electron type has a unique path where it will likely be found. Electrons orbit and remain with in specific energy rings.

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.