**Core Concept**
Uricosuric drugs increase the excretion of uric acid in the urine by inhibiting its reabsorption in the proximal renal tubules, thereby reducing serum uric acid levels. This effect is distinct from xanthine oxidase inhibitors like allopurinol, which reduce uric acid production.

**Why the Correct Answer is Right**
Probenecid competitively inhibits the organic anion transporters (OATs) in the proximal tubule, particularly OAT1 and OAT3, which are responsible for reabsorbing uric acid. By blocking these transporters, probenecid promotes uric acid excretion in urine. It is specifically used in gout management to lower serum uric acid levels when combined with lifestyle modifications or other agents.

**Why Each Wrong Option is Incorrect**
Option A: Allopurinol is a xanthine oxidase inhibitor that reduces uric acid production, not excretion. It acts upstream in purine metabolism and is not uricosuric.
Option C: Indomethacin is a nonsteroidal anti-inflammatory drug (NSAID) that inhibits cyclooxygenase (COX) enzymes and may reduce renal blood flow and uric acid excretion, potentially worsening hyperuricemia.
Option D: Aspirin, like other NSAIDs, can inhibit renal prostaglandin synthesis, leading to reduced glomerular filtration rate and decreased uric acid excretion, thus acting as a uricosuric agent in some contexts but not as a true uricosuric drug.

**Clinical Pearl / High-Yield Fact**
Probenecid is the only clinically used uricosuric agent that enhances uric acid excretion via tubular inhibition. It should be used cautiously in patients with renal impairment or dehydration due to risk of renal stones.

✓ Correct Answer: B. Probenecid