Question

What is the molar mass of any substance defined as?

Answer 1

The mole of a substance always contains the same number of entities whatever the substance may be. The molar mass is related to the mass of a substance that contains one mole or $6.022\times {{10}^{23}}$ number of entities of the substance.

Complete answer:
As to make the calculations of bulk substances easier in the real world, we take a standard value to calculate different things e.g. 1 dozen is always considered to be equal to 12 items. Similarly, we use the mole in the scientific world to calculate the size of the smallest entities quantitatively.
The mole is the measure of the quantity of any chemical entity, such as atoms, electrons, or protons. It is defined as the amount of a substance that contains as much chemical entity (atoms, molecules, or electrons) as there are in 12 grams of a pure carbon-12 atom. So, it was found that 1 mole contains $6.022\times {{10}^{23}}$ elementary entities of the substance.
Molar mass is defined as the mass of the substance present per mole. For a given amount of substance, the molar mass can be calculated by dividing the total mass of the substance by the total number of moles present in that amount.
$\text{Molar Mass (M)}=\dfrac{\text{Mass of substance}}{\text{No}\text{. of moles}}$
The molar mass is represented in the units of gram per mole $\left( \text{g mo}{{\text{l}}^{-1}} \right)$. However, the SI unit is $\left( \text{kg mo}{{\text{l}}^{-1}} \right)\text{ }$, which is very rarely used.
Hence, the molar mass of any substance is defined as the mass in grams of a substance that makes up a mole.

Note:
The atomic mass and the molar mass of atoms are numerically equal. They differ only in units; atomic mass is measured in atomic mass units, and molar mass is measured in grams per mole.