Elements in the periodic table are identified by their unique atomic numbers.
The atomic number (Z) of an element, is the count of protons present in the nucleus of the atom. The atomic mass or mass number (A) of an element, is the sum of the protons and neutrons present in the nucleus of the atom.
Isotopes are chemical species or variants of the same element having identical atomic numbers but different mass numbers.
This suggests that the number of protons in these species is the same but they differ in the number of neutrons.
Explanation:
Isotopes have wide medical applications.
Iodine has around 34 isotopes. Most of the isotopes of iodine are radioactive except 127I which is the only stable naturally occurring isotope.
131
I or Iodine-131 is a radioactive isotope used in the treatment of goiter, a disease associated with the thyroid gland.