Nuclei with the same mass number but different atomic numbers are called isobars. Consider Ca-40, Ca-41, K-41 and Ar-41. (a) Which of these are isobars? Which are isotopes? (b) What do Ca-40 and Ca-41 have in common? (c) Correct the statement (if it is incorrect) : Atoms of Ca-41, K-41, and Ar-41 have the same number of neutrons.