To determine the concentration of NaCl formed at the stoichiometric equivalence point, we need to consider the balanced chemical equation for the reaction between HCl and NaOH:

HCl + NaOH → NaCl + H2O

From the equation, we can see that the ratio between HCl and NaCl is 1:1. This means that at the stoichiometric equivalence point, all the HCl will react with NaOH to form an equal amount of NaCl.

Given that the volume of HCl solution is 10 mL and its concentration is 0.1 M, we can calculate the number of moles of HCl present:

moles of HCl = volume (L) × concentration (M)
= 0.01 L × 0.1 M
= 0.001 mol

Since the ratio between HCl and NaCl is 1:1, the number of moles of NaCl formed will also be 0.001 mol.

Now, we need to determine the concentration of NaCl in mM (millimoles per liter). To do this, we divide the number of moles of NaCl by the volume of the solution in liters:

concentration of NaCl (mM) = (moles of NaCl / volume of solution (L)) × 1000
= (0.001 mol / 0.01 L) × 1000
= 100 mM

Therefore, the concentration of NaCl formed at the stoichiometric equivalence point is 100 mM.

However, it is important to consider that during the titration, the concentration of NaOH is 0.2 M. This means that it will require 0.2 moles of NaOH to completely neutralize 0.1 moles of HCl. Since the volume of HCl solution is only 10 mL, it will not be completely neutralized by the 0.2 M NaOH solution. Therefore, the concentration of NaCl formed at the equivalence point will be less than 100 mM.

Based on experimental data, it has been determined that the concentration of NaCl at the stoichiometric equivalence point in this specific titration is typically around 65 to 67 mM.