Answer: The correct answer is Option 4.
Explanation: All the given options are radioisotopes of the respective elements. The radioisotopes are the ones which are radioactive in nature and decay after some time.
To determine human gland disorders, the radioisotope of iodine is used which is [tex]_{53}^{131}\textrm{I}[/tex]. This isotope is used because thyroid naturally contains iodine and its radioisotope is used to diagnose thyroid gland disorders.
Hence, the correct answer is option 4.