Molarity of a solution is defined as the number of moles of solute in 1 L of solution. here we are given 4 mol of NaOH to be dissolved in 2 L of water the number of moles of NaOH in 2 L of water - 4 mol therefore number of NaOH moles in 1 L of water - 4/2 = 2 mol of NaOH there are then 2 mol of NaOH in 1 L