State the difference between Atomic mass and molecular mass?

Find the molecular mass of HNO3.

Atomic mass: The mass of an atom is known as atomic mass.

Molecular mass: The sum of masses of all atoms in a molecule is known as molecular mass.

The molecular mass of HNO3 is
H= 1U N= 14U O3= (3*Atomic mass of O)
The molecular mass of HNO3 = 63U