Isotopes are atoms of the same element having the same atomic number Z but different mass number A. The nuclei 1H1, 1H2 and 1H3 are the isotopes of hydrogen. In other words isotopes of an elementcontain the same number of protons but different number of neutrons.As the atoms of isotopes have identical electronic structure, they have identical chemical properties and placed in the same location in the periodic table.
SAME ATOMIC NUMBER
BUT DIFFERENT MASS NUMBER.