Question

Atoms of different elements possessing the same atomic mass are called:

• A. Isotopes
• B. Isomers
• C. Isobars
• D. Molecules

Hint:

Isomers have the same number and types of atoms but differ in the way the atoms are arranged or bonded.

Answer 1

The Correct Option is C

• Option 1: Isotopes - This is incorrect. Isotopes are atoms of the same element that have the same atomic number but different mass numbers due to different numbers of neutrons.
• Option 2: Isomers - This is incorrect. Isomers are molecules with the same molecular formula but different structural arrangements, not atoms with the same atomic mass. 
• Option 3: Isobars - This is the correct answer. Isobars are atoms of different elements that have the same atomic mass (or mass number). Despite having different atomic numbers (protons), their mass numbers are identical.
• Option 4: Molecules - This is incorrect. Molecules are combinations of atoms, but they are not defined by having the same atomic mass.

Explanation:

Atoms of different elements that possess the same atomic mass are called isobars. Isobars have different numbers of protons (and thus belong to different elements) but have the same total mass number due to having different numbers of neutrons.

Answer 2

A concrete pair of atoms, potassium-40 and calcium-40, shows exactly what this definition is pointing at.

1. Isotopes: Potassium, with 19 protons, and calcium, with 20 protons, are different elements with different atomic numbers, so they cannot be isotopes of each other. Isotopes require the same element.
2. Isomers: This term is for molecules with an identical formula but a different structural arrangement. Single atoms like potassium-40 and calcium-40 are not molecules, so this term does not apply.
3. Isobars: Potassium-40 has 19 protons and 21 neutrons, while calcium-40 has 20 protons and 20 neutrons. Different elements, different proton counts, but the same total mass number of 40, is exactly what defines isobars.
4. Molecules: A molecule requires atoms bonded together. Two separate single atoms are not automatically a molecule, so this option does not describe the relationship being asked about.

Potassium-40 and calcium-40 are different elements sharing the same mass number, which is the defining feature of isobars.

So the correct answer is Isobars.