Answer to Question #151672 in Chemistry for Paulo

Question

Which of the following are isotopes, choose all that apply.

a) Element X with atomic number 10 and atomic mass 21
b) Element Y with atomic number 11 and atomic mass 21
c) Element Z with atomic number 10 and atomic mass 22
d) Element M with atomic number 12 and atomic mass 21

Answer 1

According to the definition, the isotopes are the variants of the same element which differ in neutron number in their nuclei and therefore in their atomic mass. At the same time, the atomic number, that corresponds to the number of protons in the nucleus, is the same for different isotopes.

Among the proposed elements, only X and Z (a and c) have the same atomic number, 10, and different atomic masses, 21 and 22, respectively. Therefore, only the elements X and Z (a and c) are isotopes.