Why you may need less than one liter of water to prepare a molar solution of one liter?

You may need less than one liter of water to prepare a one-liter molar solution because the solute being dissolved contributes to the total volume of the solution. When a solute is added to the solvent, the final volume is the sum of the volume of the solvent and the volume of the solute, which means the total volume may exceed one liter. Thus, you can start with slightly less than one liter of water to account for the volume of the solute and ensure the final solution reaches the desired one-liter mark.