To solve this problem, we can use the concept of stoichiometry and the balanced chemical equation for the reaction between hydrochloric acid HCl and sodium hydroxide NaOH :HCl aq + NaOH aq NaCl aq + H2O l From the balanced equation, we can see that the mole ratio between HCl and NaOH is 1:1. This means that one mole of HCl reacts with one mole of NaOH.First, let's find the moles of NaOH used in the reaction:moles of NaOH = volume L concentration M moles of NaOH = 0.025 L 0.1 M = 0.0025 molesSince the mole ratio between HCl and NaOH is 1:1, the moles of HCl will also be 0.0025 moles.Now, we can find the concentration of HCl using the formula:concentration M = moles of solute / volume of solution L Let the concentration of HCl be x M. Then,x M = 0.0025 moles / 0.020 Lx = 0.125 MSo, the concentration of hydrochloric acid HCl in the solution is 0.125 M.