The pH of a 0.001 M HCL solution is 3.
According to this calculation, the initial concentration of HCl is 1 x 10^-3 M. If we assume that this acid dissociates completely, the [H3O+] ion concentration at equilibrium is 1 x 10^-3 M. The solution prepared by adding one drop of 2 M HCl to 100 mL of water would therefore have a pH of 3.
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