The difference is due to the degree of dissociation of the substances. HCl dissociates completely into ions when added to water, while this is not the case for HC₂H₃O₂; therefore, HCl has a lower pH.
B) The elements become less reactive.
The correct answer is B. The concentration of a solution does not decreases when you add more solute to the solvent. Instead, the concentration increases. Concentration is expressed as the amount of solute per unit of solvent. Therefore, increasing the solute, increases this value and increasing the solvent, decreases this value.
