In an experiment a piece of magnesium ribbon was cleaned with steel wool.2.4g of the clean magnesium ribbon was placed in a crucible and completely burnt in oxygen. After cooling the product weighed 4.0g. (a)What observation was made in the crucible after burning magnesium ribbon
(b)Why was there an increase in mass
(c)write a chemical equation and a word equation for the major chemical reaction which took place in the crucible

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.