<u>Answer: </u>The correct answer is Option D.
<u>Explanation:</u>
Unstable isotopes are defined as the isotopes which have excess of neutrons as compared to the stable form of the nucleus of an atom.
These isotopes attain stability by undergoing a spontaneous nuclear decay. The isotopes which are unstable have another name and are known as radioactive isotopes or radioisotopes.
These isotopes undergoes decay by 4 processes: Alpha decay, beta decay, gamma emission and positron decay.
Hence, the correct answer is option D.
