What does molar mass indicate?

The correct option accurately reflects that molar mass is defined as the mass of one mole of a substance, measured in grams per mole (g/mol). This concept is central to stoichiometry in chemistry, where molar mass allows chemists to convert between the mass of a substance and the number of moles present. Knowing the molar mass is essential for calculations involving chemical reactions, where substances react in fixed proportions based on their mole ratios.

For instance, if you have the molar mass of water (approximately 18 g/mol), this means that one mole of water has a mass of 18 grams. This relationship enables chemists to accurately measure and combine reactants in reactions, ensuring successful processes in both laboratory and industrial settings.

The other choices refer to different concepts: the volume of one mole of a gas pertains to the ideal gas law under standard conditions, the number of moles in a solution relates to the molarity and concentration of a substance, and density is a property of matter that relates mass and volume but does not encompass the concept of moles directly. Thus, this choice captures the definition of molar mass precisely and its application in chemical calculations.