Answer:
pH value of a solution depends on the concentration of hydrogen ions
(pH = -log[H+(aq)].
Hydrochloric acid is a strong acid, while ethanoic acid is a weak acid. Strong acids ionize completely in water (to give ions which includes H+(aq)), while weak acids only ionize partially in water.
Therefore, even if both hydrochloric acid and ethanoic acid are monobasic acids (each molecule can ionize completely to give 1 hydrogen ion), since hydrochloric acid ionizes completely in water and ethanoic acid does not ionize completely, the concentration of hydrogen ions in hydrochloric acid is higher than that of ethanoic acid, leading to a lower pH value for hydrochloric acid, while higher for ethanoic acid.
