A sample of limestone (impure calcium carbonate) weighing 0.20g was reacted with 50cm' of 0.10mol dm3 hydrochloric acid.
CaCO3(s) + 2HCl(aq) → CaCl2(aq) + CO2(g) + H2O()
The hydrochloric acid was in excess, and the excess HCl(aq) reacted with 14cm of 0.10 mol dm3 sodium
hydroxide. Calculate the percentage by mass of calcium carbonate in the limestone

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.