**Core Concept**
Gout is a form of inflammatory arthritis characterized by the deposition of monosodium urate crystals within the joint space, leading to intense pain, swelling, and redness. Accurate diagnosis of gout requires identification of these crystals in the synovial fluid of the affected joint.

**Why the Correct Answer is Right**
The correct answer is B, as the presence of urate crystals in the synovial fluid is a definitive diagnostic criterion for gout. This is because the synovial fluid is in direct contact with the joint space where the crystals accumulate. To confirm the diagnosis, a synovial fluid analysis is performed, which involves aspiration of fluid from the affected joint and examination under polarized light microscopy. The presence of negatively birefringent needle-like crystals is a hallmark of gout. The synovial fluid analysis is considered the gold standard for diagnosing gout.

**Why Each Wrong Option is Incorrect**
**Option A:** Raised serum uric acid level is a common finding in gout but is not specific for the disease. Many patients with gout have normal serum uric acid levels, and elevated levels can also be seen in other conditions such as kidney disease or chemotherapy.

**Option C:** Raised urea level is not related to gout and is more commonly associated with renal impairment or dehydration.

**Option D:** Raised urease enzyme level is not relevant to the diagnosis of gout. Urease is an enzyme involved in the breakdown of urea, and its level is not a diagnostic criterion for gout.

**Clinical Pearl / High-Yield Fact**
In addition to synovial fluid analysis, other diagnostic criteria for gout include acute onset of joint pain, redness, swelling, and tenderness, often occurring at the base of the big toe (podagra). A history of similar episodes and the presence of tophi (urate deposits) on radiographs or physical examination can also support the diagnosis of gout.

**✓ Correct Answer: B. Raised uric acid in synovial fluid of joint**