**Core Concept**
Multiple myeloma is a clonal plasma cell disorder characterized by the proliferation of malignant plasma cells in the bone marrow, leading to an increase in monoclonal immunoglobulin production. This results in various metabolic and skeletal abnormalities.

**Why the Correct Answer is Right**
Option **c**) is incorrect because hypercalcemia in multiple myeloma is primarily caused by the increased osteoclast activity and bone resorption, not by elevated serum alkaline phosphatase. Elevated alkaline phosphatase is typically associated with bone formation and is more characteristic of conditions such as Paget's disease or bone metastases. In contrast, hypercalcemia in multiple myeloma is due to the unregulated activity of osteoclasts, which is mediated by the RANKL/RANK/OPG pathway.

**Why Each Wrong Option is Incorrect**
**Option A:** Hypercalcemia is indeed a common feature of multiple myeloma, often resulting from bone destruction and increased osteoclast activity.
**Option B:** Hyperuricemia is also seen in multiple myeloma, resulting from the increased turnover of nucleic acids and the subsequent breakdown of nucleotides to uric acid.
**Option D:** Monoclonal M band is a characteristic feature of multiple myeloma, representing the abnormal immunoglobulin produced by the malignant plasma cells.
**Option E:** Bone marrow plasma cell count 10% of the total bone marrow cellularity.

**Clinical Pearl / High-Yield Fact**
Multiple myeloma should be suspected in patients with a history of recurrent infections, bone pain, or unexplained hypercalcemia, particularly in the context of anemia and a monoclonal spike on serum protein electrophoresis (SPEP).

**Correct Answer: C. ↑ Serum alkaline phosphatase**