Q. Which of the following acid is secreted in the stomach ?

The correct answer is: d) Hydrochloric acid.

Explanation: The stomach secretes hydrochloric acid (HCl) as part of the gastric juice. This acid plays a crucial role in digestion by creating an acidic environment in the stomach. It helps in breaking down food, activating digestive enzymes like pepsin, and killing harmful bacteria or pathogens that may enter the stomach with food.

Hence, the correct answer is hydrochloric acid.