How is the molarity of a solution calculated?

Molarity is fundamentally defined as the concentration of a solution expressed in terms of the amount of solute present in a given volume of solution. This concept is quantified as the number of moles of solute divided by the volume of the solution in liters. Therefore, the correct method to calculate molarity is to take the number of moles of solute and divide that by the liters of solution. This allows for a standardized way to express concentration, facilitating comparisons and calculations in various chemical contexts.

The other options do not accurately represent the definition of molarity. For instance, calculating grams of solute per liter of solution does not consider the molar mass of the solute, which is necessary to convert grams to moles. Multiplying moles of solute by the volume of the solution does not yield a concentration; rather, it results in a product that is unrelated to molarity. Similarly, multiplying liters of solution by grams of solute does not provide information about concentration because it lacks the necessary conversion to moles. Thus, the correct representation of molarity aligns perfectly with option A.