[Kartiky14]

What is the difference between actual mass of an atom and gram atomic mass? And is atomic mass different from the actual or absolute atomic mass of an atom?

"As explained in the textbook that gram atomic mass is the quantity of an element in grams which is numerically equal to the atomic mass"

How is that ?

[Sophia7X]

It's just how scientists define it.

6.022x10²³ amu = 1g.
Oxygen's atomic mass is 16 amu.
The definition of molar mass/gram atomic mass is the mass of one mole of atoms.

1 mol of O = 6.022x10²³ atoms.
Therefore,  6.022x10²³ atoms O * (1 gram/6.022x10²³ amu ) = 16 grams/mol. This is how atomic mass can equal molar mass.