The value of the Avogadro number is 

Avogadro’s number (N_A) is defined as the number of units in 1 mole of that substance and it is equal to $6.022\times {10}^{23}$.

Units can be atoms, particles, molecules, or any type of constituent.

The value of Avogadro's constant was chosen so that the mass of one mole of a chemical compound in grams is numerically equal (for all practical purposes) to the average mass of one molecule of the compound in daltons (universal atomic mass units); one Dalton being 1/12 mass of one carbon-12 atom, which is approximately the mass of one nucleon (proton or neutron).

For example, the average mass of one water molecule is about 18.0153 daltons, and one mole of water (N molecules) is about 18.0153 grams. Thus, Avogadro's constant N_A is a proportionality factor that relates the molar mass of a substance to the average mass of one molecule.

Hence, the correct option is (B).