Step 1: Recall what triggers an allergic reaction.
Allergies happen when IgE antibodies coat mast cells and basophils, and a later encounter with the same allergen makes these cells burst open their granules.
Step 2: Recall what those granules contain.
The stored chemicals released during this degranulation are the ones responsible for the classic allergy symptoms like swelling, redness and itching.
Step 3: Name the chemicals.
Histamine widens blood vessels and tightens airways, while serotonin adds to the vessel leakiness, together producing the visible allergic response.
Final answer: Option 3, Histamine and Serotonin.