A laboratory was using some faulty equipment and some of the chemicals leaked out, which produced only 6.51 grams of sodium chloride when HCl was reacted with
NaOH. The theoretical yield for such a reaction is normally 10.64 grams, find the
percent yield.

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.