The atomic number of calcium and argon are 20 and 18 respectively, but the mass number of both these elements is 40. What is the name given to such a pair of elements?
Atoms of different elements which have the same mass number but have different atomic numbers are called isobars. For example, calcium, atomic number-20 and argon, atomic number 18 are isobars. Both these elements have same mass number which is equal to 40. Therefore, the total number of nucleons is the same in both the elements.