The addition of water to a solution of oxalic acid will affect the molarity of the solution. This is because molarity is defined as the number of moles of solute per liter of solution. When water is added to a solution, the volume of the solution increases, which means that the concentration of the solute decreases. This decrease in concentration results in a lower molarity.

For example, if you have a 1 molar solution of oxalic acid and you add 1 liter of water to it, the volume of the solution will double to 2 liters. The number of moles of oxalic acid will remain the same, so the molarity of the solution will decrease to 0.5 molar.

The amount by which the molarity decreases depends on the amount of water that is added. The more water that is added, the greater the decrease in molarity.