Molecular mass is the weight of a molecule calculated by adding the total atomic mass of each constituent multiplied by the number of atoms in a given molecule of a compound.
In this case, C= 12, O=16, H= 1, in ethanol there are 6 atoms of hydrogen, 2 atoms of carbon and 1 atom of oxygen.
Therefore, mass = (12×2) + (16×1) + (1×6) =46
hence, the molecular mass of ethanol is 46