The correct answer is option 4, gastric juice. Gastric juice is a digestive fluid produced by the stomach. It consists of hydrochloric acid (HCl) and other enzymes that help break down food and kill bacteria in the stomach. Hydrochloric acid is a strong acid that readily ionizes in water, releasing a large amount of hydrogen ions (H+).
Option 1, sodium hydroxide solution, is a strong base. Bases do not release hydrogen ions, but instead, they can accept them. Therefore, it does not give a high amount of hydrogen ions.
Option 2, milk of magnesia, is an alkaline suspension containing magnesium hydroxide. Like sodium hydroxide, it is a base and does not release a significant amount of hydrogen ions.
Option 3, lemon juice, is acidic but is not as strong as gastric juice. Lemon juice contains citric acid, which can release hydrogen ions, but the concentration of hydrogen ions in lemon juice is lower compared to gastric juice.
Overall, gastric juice from the stomach contains a high concentration of hydrochloric acid and gives the highest amount of hydrogen ions among the given options.