**Core Concept:** Heinz bodies are intracytoplasmic, non-dissociable, red blood cell pigment granules formed due to auto-oxidation of hemoglobin, mainly in the presence of acidic conditions and low oxygen tension.

**Why the Correct Answer is Right:** Heinz bodies are formed from the non-dissociable, intravascular breakdown products of hemoglobin. In acidic conditions, such as those found in the presence of certain drugs (e.g., sulfa drugs), the α-globin chains and β-globin chains of hemoglobin do not dissociate, leading to the formation of Heinz bodies. These bodies are composed of both chains, making option D the correct answer.

**Why Each Wrong Option is Incorrect:**

A. Hemoglobin dissociates into its constituent chains (α-globin and β-globin) under normal physiological conditions, making this option incorrect.
B. While acidosis can lead to Heinz body formation, it is not the sole cause.
C. Hemoglobin dissociates into its constituent chains under normal physiological conditions, making this option incorrect as well.

**Clinical Pearl:** Heinz bodies are a crucial clinical pointer in diagnosing red cell hemolysis and can be seen in various conditions like iron deficiency anemia, drug-induced hemolysis, and autoimmune hemolysis.

**Correct Answer:** D. Hemoglobin

**Explanation:** Heinz bodies are intracytoplasmic, non-dissociable, red blood cell pigment granules formed due to auto-oxidation of hemoglobin, mainly in the presence of acidic conditions and low oxygen tension. This leads to the formation of non-dissociable α-globin chains and β-globin chains of hemoglobin, which are then assembled to form Heinz bodies.