What does the second law of thermodynamics say about entropy? A. Only changes in entropy can be measured.
B. Entropy cannot be created or destroyed.
C. The entropy in a system is zero at equilibrium.
D. The entropy in a system and its surroundings tends to increase.

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.