What is the Mr in chemistry?

In chemistry, "Mr" stands for molar mass, which is the mass of one mole of a substance, typically expressed in grams per mole (g/mol). It is the sum of the atomic masses of all the atoms in a molecule, calculated from the Periodic Table. Molar mass is essential for stoichiometric calculations in chemical reactions, allowing chemists to convert between moles and grams of a substance.