What is the definition of molarity in chemistry?

Molarity is defined as the number of moles of solute dissolved in one liter of solution. This unit of concentration specifically indicates how much of a substance is present relative to the volume of the solution it is in. Molarity is commonly expressed in units of moles per liter (mol/L), making it a crucial concept in stoichiometry and various chemical calculations where understanding concentrations is essential.

The other options do not correctly represent the definition of molarity. The mass of solute per liter of solution, while related to concentration, refers to molarity's counterpart—mass concentration, which utilizes grams instead of moles. Similarly, measuring the volume of solute does not account for the total volume of the solution and is not a standard way to determine concentration. Lastly, the number of molecules in a solution does not directly translate into molarity without converting to moles, as molarity specifically requires this conversion to relate to volume. Thus, the definition as moles of solute per liter of solution is not only precise but fundamental in understanding how substances interact in a solution.