When heated, calcium carbonate goes through a chemical reaction, and produces calcium oxide (quick lime) powder and carbon dioxide gas. A chemist performed this reaction in a lab and found that the mass of the calcium oxide (quick lime) was less than the mass of the calcium carbonate. What is the reason behind this decrease in mass?

b) nuclear ive learned that in a pedtrodic table

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.