Gram Atom of an element is defined as the atomic mass expressed in grams. For example, atomic mass of C is 12 amu. If we take 12 g of Carbon, it will be 1 gram atom of C.

Importance of the concept of gram atom 

We cannot see an atom and will never see it with naked eye. Weighing it is yet another impossibility! On the other hand, we can see and weigh one gram-atom of an element. Now, one gram atom contains a known number of atoms, called Avogadro’s number. So the concept of gram atom gives us a better understanding of the role of an atom in a chemical reaction.