What do you mean by formula unit mass, molecular mass? give an example of each.

Molecular Mass: The Molecular mass of a substance is the sum of the atomic masses of all the atoms in a molecule of the substance.
So, we can simply use the molecular formula to calculate the molecular mass. For example-
The molecular mass of water (CH₄) will be the sum of the atomic mass of four atoms of hydrogen
and the atomic mass of one atom of carbon.
Molecular mass = Atomic mass of four hydrogen atoms + Atomic mass of one carbon atom

= 4 X 1 + 1 X 12

= 16 u

Formula unit mass: The formula unit mass of a substance is the sum of the atomic masses of all atoms in a formula unit
of a compound.
For Example -

Formula unit mass of calcium chloride (CaCl₂) =  Atomic mass of Ca + 2 X atomic mass of Cl

= 40 + 2 X 35.5 

= 40 + 71

111 U