How do i find the isotopic notation?

Explanation :

Isotope : It is defined as the element that have the same number of protons but have the different number of neutrons of each of the atom.

Isotope notation : It is also called as nuclear notation. In isotopic notation we can easily determine an isotope's mass number, atomic number, the number of neutrons and protons in the nucleus.

The general isotopic representation of an atom is:

where,

Z = Atomic number of the atom

A = Mass number of the atom

X = Symbol of the atom

For example : atom.

From this we conclude that,

Atomic number of Ni atom = 28

Mass number of Ni atom = 64

The symbol of atom = Ni

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.