Atoms

Step 1: Understanding Vasodilators
Vasodilators are substances that widen blood vessels, reducing blood pressure.
Histamine plays a key role in immune response and vasodilation.
Step 2: Classification of Given Options
Histamine causes vasodilation and regulates stomach acid secretion.
Serotonin affects mood and blood clotting but is not a vasodilator.
Codeine is an opioid pain reliever.
Cimetidine is a histamine receptor
blocker.
Final Answer: Since histamine is the primary vasodilator, the correct answer is (A).