Answer:
B
Explanation:
Isotopy is a phenomenon in which there exists two or more kind of atoms of the same element. These atoms have the same number of protons but different mass numbers. That is, they have the same atomic number but differ only by the number of neutrons in the nucleus of the atom. Now, let us apply this information to the options individually:
A. Is wrong, they are not the same element
B. Is correct. they both belong to the same element hydrogen. Infact, they are named protium and deuterium respectively
C is wrong they are not same element
D is wrong They are not elements at all
E. Is wrong, one is an element, the other is a molecule
