1. Write the balanced chemical equation:

HCl (aq) + NaOH (aq) → NaCl (aq) + H₂O (l)

2. Determine the moles of NaOH used:

* Molarity (M) = moles (mol) / volume (L)

* Moles of NaOH = Molarity * Volume

* Moles of NaOH = 0.24 M * 0.035 L = 0.0084 mol

3. Use stoichiometry to find moles of HCl:

* From the balanced equation, 1 mole of HCl reacts with 1 mole of NaOH.

* Therefore, the moles of HCl are equal to the moles of NaOH: 0.0084 mol HCl

4. Calculate the concentration of HCl:

* Molarity of HCl = moles of HCl / volume of HCl

* Molarity of HCl = 0.0084 mol / 0.050 L = 0.168 M

Therefore, the concentration of the HCl solution is 0.168 M.