Explain how it is possible for two different elements to have the same mass number

Atoms from two different elements may have the same number of neutrons, but never the same number of protons

Atoms of an element with the same mass number make up an isotope of the element. Different isotopes of the same element cannot have the same mass number, but isotopes of different elements often do have the same mass number, e.g., carbon-14 (6 protons and 8 neutrons) and nitrogen-14 (7 protons and 7 neutrons).