Why is it that the relative atomic mass of an atom is numerically equal to gram atomic mass?
For example,Relative Atomic Mass of Oxygen= 16 u So,Gram atomic mass of Oxygen=16 g.
The relative atomic mass of an atom is its mass relative to an atom of carbon-12 (which is 12 by definition). A mole of carbon 12 atoms weighs 12g (which is where the definition comes from).
"Gram atomic mass" is just an alternative way for saying the mass of a mole of some atom. So the ratio of the atomic masses will always be the same regardless of how many of the atoms you are counting. Hence, the two ideas are numerically the same.