The sum of the atomic masses of all the atoms in a molecule of the substance is-

Correct option is D

The correct answer is (d) Molecular mass.
Molecular mass: The molecular mass (also known as molecular weight) is the sum of the atomic masses of all the atoms in a molecule of a substance. It is calculated by adding together the atomic masses of each element in the molecule, multiplied by the number of atoms of that element in the molecule. Molecular mass is typically expressed in atomic mass units (amu).
For example, the molecular mass of water (H₂O) is calculated as follows:
· Hydrogen (H) has an atomic mass of approximately 1 amu. There are 2 hydrogen atoms in a molecule of water, contributing a total of 2 amu.
· Oxygen (O) has an atomic mass of approximately 16 amu. There is 1 oxygen atom in a molecule of water, contributing 16 amu.
· Therefore, the molecular mass of water is 2×1+16=18 amu.