**Core Concept**
Ibuprofen is a nonsteroidal anti-inflammatory drug (NSAID) that works by inhibiting the enzyme cyclooxygenase (COX), which plays a crucial role in the synthesis of prostaglandins. This mechanism is essential for its anti-inflammatory, analgesic, and antipyretic effects.

**Why the Correct Answer is Right**
Ibuprofen selectively inhibits COX-2, an enzyme responsible for the production of prostaglandins in response to inflammation. By blocking COX-2, ibuprofen reduces the formation of prostaglandins, which are mediators of inflammation, pain, and fever. This action is crucial for its therapeutic effects in treating conditions such as arthritis, muscle pain, and fever.

**Why Each Wrong Option is Incorrect**
**Option A:** Ibuprofen does not primarily act on the enzyme lipoxygenase, which is involved in the synthesis of leukotrienes. Lipoxygenase inhibitors are a different class of anti-inflammatory drugs.
**Option B:** Ibuprofen does not primarily act on the enzyme phospholipase A2, which is involved in the release of arachidonic acid, a precursor to prostaglandins. While phospholipase A2 inhibitors may have some anti-inflammatory effects, they are not the primary mechanism of action for ibuprofen.
**Option C:** Ibuprofen does not primarily act on the enzyme cyclooxygenase-3 (COX-3), which is a hypothetical enzyme that has not been widely accepted as a valid target for NSAIDs.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that NSAIDs like ibuprofen can cause gastrointestinal irritation and bleeding due to their inhibition of COX-1, which is involved in the production of protective prostaglandins in the stomach lining.

**Correct Answer:** C. Ibuprofen acts on cyclooxygenase (COX) enzymes.