Which one item of the list below does not describe part of beta decay? A. The nucleus of the atom is unstable.
B. A neutron turns into a proton.
C. A proton turns into an electron.
D. An electron is ejected from the nucleus.

C

Explanation:

When Beta decay happens, the atomic number of an element goes up, and that means there is an extra proton. A is not the answer because unstable atoms cause decay. B is also not correct because this is what happens in Beta decay: a neutron becomes a proton. D is not correct because an electron is actually emitted from the nucleus.

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.