Can someone explain this to me?

it says how to make an atom stable like ion if the atom is metal then it will lose the atom to be full outer shell and if it is non metal it will gain.

second thing there is also covalent bond which share electron with other atomto be full outer shell

hope this help!!

radioactive decay occurs in unstable atomic nuclei – that is, ones that don't have enough binding energy to hold

the nucleus together due to an excess of either protons or neutrons.

i believe the answer is a.