**Core Concept**
Pseudogout, also known as calcium pyrophosphate deposition disease (CPPD), is a type of arthritis characterized by the accumulation of calcium pyrophosphate dihydrate (CPPD) crystals within the joint space. This condition leads to inflammation and pain, mimicking gout but caused by a different type of crystal.

**Why the Correct Answer is Right**
The correct answer is made up of calcium pyrophosphate dihydrate (CPPD) crystals, which are deposited in the joint space and cause inflammation. This process is often triggered by metabolic disorders, aging, or other underlying conditions. The CPPD crystals stimulate an immune response, leading to the release of pro-inflammatory cytokines and the recruitment of white blood cells, resulting in joint pain and swelling.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specify the correct composition of pseudogout crystals. While calcium pyrophosphate dihydrate is a key component, the term "calcium crystals" is too broad and does not accurately describe the specific type of crystal responsible for pseudogout.

**Option B:** This option is incorrect because it refers to the crystals found in gout, which are composed of monosodium urate (MSU). Gout and pseudogout are distinct conditions with different underlying causes and manifestations.

**Option C:** This option is incorrect because it does not accurately describe the composition of pseudogout crystals. While calcium is a component of the crystals, the specific type of calcium compound responsible for pseudogout is calcium pyrophosphate dihydrate, not calcium phosphate.

**Clinical Pearl / High-Yield Fact**
The key to distinguishing pseudogout from gout is the type of crystal found in the joint space. While both conditions are characterized by the accumulation of crystals, the specific composition of the crystals is a critical diagnostic clue.

**Correct Answer:** C. Calcium pyrophosphate dihydrate (CPPD) crystals.