Assign oxidation numbers to each atom in KBrO4

K: +1

Br: +7

O: -2

Explanation:

O is always -2

K is in group one, so that is its charge

-8+1 is -7, so we flip the sign and that becomes Br

The reason why we flip it is to get a net balance of 0

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.