Answer: These two nucleotides are termed as isotopes.
Explanation: Isotopes are the species of the same element having same number of protons and electrons but different number of neutrons.
Atomic number remains same but their atomic masses are different.
These two nucleotides are the isotopes of Iodine having atomic number 53.
 and
 and 
 are classified as Isotopes of Iodine.
 are classified as Isotopes of Iodine.