Which of the following pairs are isotopes?

Question

A. Carbon-14 and Nitrogen-14

B. Hydrogen-3 and helium-3

C. Iron-56 and iridium-192

D. Gallium-69 and gallium-70

Answer 1

Hey Shai!

Isotopes are elements of the same chemical identity (ex. Nitrogen), but with different masses. This is because of a difference in the number of neutrons that the isotopes have. Isotopes will always have the same number of protons, but a different number of neutrons.

A. Choice A has 2 different elements, which means that they cannot be isotopes, as isotopes are variants of the same element.

B. Choice B also has 2 different elements, which means they are not isotopes of one another.

C. Choice C also deals with 2 different elements, meaning they are not isotopes of each other.

D. Choice D deals with the same element. The -69 refers to the mass of the isotope of Gallium-69 being 69 amu. Gallium-70 has a mass of 70 amu. Because isotopes by definition have the same chemical identity (Gallium in this case), but different atomic masses (69 vs 70 amu), Choice D is the correct answer.

Hope this helps!