Explanation:

- The correct answer is Option 3: Hydrochloric acid.

- Hydrochloric acid is present in the stomach and helps in digestion by breaking down food.

- It creates an acidic environment that activates enzymes like pepsin for protein digestion.

- Option 1: Nitric acid

- Nitric acid is a strong and corrosive acid not involved in digestion.

- Mainly used in industrial processes like manufacturing fertilizers.

- Option 2: Acetic acid

- Found in vinegar and used as a preservative and in cooking.

- Not involved in digestion within the human body.

- Option 4: Sulphuric acid

- A strong and corrosive acid used in industries and car batteries.

- Not involved in digestion.