Step 1: Cause of stomach pain and irritation.
Pain and irritation in the stomach are generally caused by excess secretion of hydrochloric acid in the gastric juice.
Step 2: Role of antacids.
Antacids are substances that neutralize excess stomach acid, thereby relieving pain, irritation, and discomfort.
Step 3: Elimination of other options.
Tranquilizers affect the nervous system, antibiotics kill bacteria, and antiseptics prevent infection on wounds. None of these neutralize stomach acid.
Step 4: Conclusion.
Thus, the correct answer is (D) Antacid.