Elements with different atomic numbers but the same mass are called isobars. The term "isobar" comes from the Greek words "isos" meaning "equal" and "baros" meaning "weight" or "mass." Isobars have different numbers of protons and electrons but the same total number of nucleons (protons plus neutrons).
there are no known stable isobars in the periodic table. However, there are a few short-lived radioactive isotopes that are isobars. For example:
Potassium-40 (K-40) and Argon-40 (Ar-40): Potassium-40 undergoes a process called beta decay and transforms into Argon-40. Both isotopes have a mass number of 40, but potassium-40 has an atomic number of 19 (19 protons) while argon-40 has an atomic number of 18 (18 protons).
Calcium-40 (Ca-40) and Titanium-40 (Ti-40): Similarly, calcium-40 and titanium-40 both have a mass number of 40, but calcium-40 has an atomic number of 20 (20 protons) while titanium-40 has an atomic number of 22 (22 protons).
These are just a couple of examples of isobars, but it's important to note that isobars are relatively uncommon in nature due to the varying stability and availability of different isotopes. The majority of elements in the periodic table do not have isobars with other elements.