 We already know that atoms of the same element having the same atomic number can have different mass numbers and such atoms are called isotopes. We have seen examples of these isotopes. So we can have these examples says carbon 12, 13 and 14. Now in each of these case they have the same atomic number that is 6 but their mass numbers are different. It's 12 for C12, 13 for C13 and 14 for the last one. Now atoms of the same element can have different mass numbers but can atoms of different element, can they have the same mass number? Well it turns out some of the atoms of different elements do have the same mass number and they are called isobars. So let's have a look at some of the examples of isobars. We can have a calcium atom. So I hope you are familiar with this form of representation of an element. If not we can have a quick glance to it. So 40 at the top this is really the mass number. This is the mass number of the element. And 20 at the bottom this is the atomic number of the element. So for calcium the mass number is 40 and the atomic number is 20. Now that means that the number of protons in a calcium atom it's 20. It has 20 protons. And mass number is really the sum of protons and neutrons. Now if protons are 20 the neutrons would be 40 minus 20. So this one has 20 neutrons and now the mass number comes out to be as 14. Let's take one more atom. We can have argon which is 40 the mass number. Proton number or the atomic number is 18 and this is the symbol of the element. Now in this case we can see that the number of protons they are 18 but the number of neutrons are really 40 minus 18. So that is 22 neutrons and again the mass number is still 40. So you can see that these are atoms of two different elements but they have the same mass number that is 40 which means we can extend it to say that they have the same atomic mass because the mass of protons and neutrons are almost they are almost the same. So if the mass number is the same the atomic mass has to be the same. We can also add potassium to this to this list. So this will be potassium has it has 19 protons and 21 neutrons again the mass number is 40. So these three are examples of isobars of different elements atoms of different elements but with the same mass number.