1thomson's plum pudding model was based on all but one of these beliels that is
al atoms are neutral
an atom has positive and negative charges
negative charges balance positive charges.
positive charges are embedded in a negative sphere.
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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.

i believe the answer is 5,000