**Core Concept**
Bence Jones protein is an abnormal protein found in the urine of patients with certain types of plasma cell dyscrasias, such as multiple myeloma. It is composed of light chains of immunoglobulins, which are produced by neoplastic plasma cells.

**Why the Correct Answer is Right**
Bence Jones protein is composed of monoclonal light chains, specifically either kappa (κ) or lambda (λ) light chains, which are produced in excess by clonal plasma cells. These light chains are not adequately assembled into complete immunoglobulins and are instead excreted in the urine. The presence of Bence Jones protein in the urine is a diagnostic clue for plasma cell dyscrasias, such as multiple myeloma or Waldenström's macroglobulinemia.

**Why Each Wrong Option is Incorrect**
**Option A:** Monoclonal heavy chains are not typically found in Bence Jones protein, as heavy chains are usually incorporated into complete immunoglobulins.
**Option C:** While both monoclonal heavy and light chains are produced in excess in plasma cell dyscrasias, Bence Jones protein specifically refers to monoclonal light chains.
**Option D:** Bence Jones protein is indeed a specific type of abnormal protein, so "none of the above" is incorrect.

**Clinical Pearl / High-Yield Fact**
Bence Jones protein is a valuable diagnostic clue for plasma cell dyscrasias, which can present with a range of symptoms including anemia, bone pain, and recurrent infections. The presence of Bence Jones protein in the urine should prompt further investigation, including serum protein electrophoresis and bone marrow biopsy.

✓ Correct Answer: B. Monoclonal light chains