The nuclides i-131 and i-133 are classifieds as
a) isomers of the same element
b) isomers of xe-131 and cs-133
c) isotopes of the same element
d) isotopes of xe-131 and cs-133

Isotopes are two atoms with the same number of protons, but a different number of neutrons. Because they have the same number of proton they are atoms of the same element, but with different masses.
so, the answer is c.
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