When an atom releases gamma radiation,
a. the mass number decreases by one.
b. the atomic number decreases by one.
c. the mass number increases by four.
d. the atomic number remains the same.

it forms an anion that has a larger radius. anions have a negative charge and are larger than the original atom.

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.