Which one of the following gives the highest amount of hydrogen ions (H+)?
The pH of gastric acid is 1.5 to 3.5 in the human stomach lumen, the acidity being maintained by the proton pump H+/K+ ATPase.
Gastric acid has a pH of between 1-2. Lemon juice has a pH of 2-3. That will dilute (lower the acidity) of stomach acid, but that acid will be neutralised in the small intestine by the presence of and production of bicarbonates.
The correct option is D.