**Core Concept**
Aplastic anemia is a rare, potentially life-threatening disease characterized by bone marrow failure to produce blood cells, resulting in pancytopenia (reduced numbers of red and white blood cells, and platelets). This condition is often the result of bone marrow damage due to exposure to toxins, radiation, or autoimmune disorders.

**Why the Correct Answer is Right**
The patient's presentation of anemia (Hb 8 gm%), leukopenia (WBC count 2000/mm3), and thrombocytopenia (platelet count 60000/mm3) is consistent with pancytopenia, a hallmark of aplastic anemia. The bone marrow's inability to produce blood cells leads to a decrease in all three cell lines, making option C the most likely diagnosis. Aplastic anemia can be triggered by exposure to certain toxins, chemotherapy, or radiation, which can damage the bone marrow and lead to its failure.

**Why Each Wrong Option is Incorrect**
**Option A:** Thalassemia is a genetic disorder affecting hemoglobin production, typically presenting with microcytic anemia, but it does not typically cause pancytopenia or thrombocytopenia.

**Option B:** Sickle cell anemia is a genetic disorder affecting hemoglobin production, leading to sickling of red blood cells, but it does not typically cause pancytopenia or thrombocytopenia.

**Option D:** Anemia of chronic disease is a condition characterized by anemia in the setting of chronic inflammation, often seen in patients with chronic infections, autoimmune disorders, or malignancies. While it can cause anemia, it does not typically cause pancytopenia or thrombocytopenia.

**Clinical Pearl / High-Yield Fact**
Aplastic anemia is a medical emergency that requires prompt treatment, often with immunosuppressive therapy, bone marrow transplantation, or supportive care. Early recognition and treatment are crucial to prevent complications and improve outcomes.

**✓ Correct Answer: C. Aplastic anemia**