**Core Concept**
The underlying principle being tested is the management of severe anemia in a pediatric patient, particularly focusing on the immediate need to improve oxygen delivery to tissues and alleviate symptoms of congestive heart failure. This scenario requires an understanding of **pediatric emergency medicine** and **transfusion medicine**. The child's severe anemia and congestive heart failure indicate a critical need for rapid intervention.

**Why the Correct Answer is Right**
Given the severe anemia (Hb = 2 gm%) and congestive heart failure, the most appropriate immediate therapy would involve improving the child's oxygen-carrying capacity and reducing the workload on the heart. This typically involves **blood transfusion**, which can rapidly increase the hemoglobin level, thereby improving oxygen delivery to tissues and potentially alleviating some symptoms of heart failure by reducing the cardiac output demand.

**Why Each Wrong Option is Incorrect**
**Option A:** Without knowing the specifics, any option not involving immediate correction of anemia and support of cardiac function would be less appropriate.
**Option B:** Similarly, any option not directly addressing the severe anemia and heart failure would not be the most appropriate immediate therapy.
**Option C:** An option that does not prioritize the urgent need to improve oxygen delivery and reduce cardiac workload would be incorrect.
**Option D:** Any option that delays necessary intervention for severe anemia and heart failure would be inappropriate.

**Clinical Pearl / High-Yield Fact**
In cases of severe anemia, especially with evidence of cardiac compromise, **prompt blood transfusion** is crucial to prevent further tissue hypoxia and cardiac decompensation. It's essential to monitor the patient closely during transfusion for signs of overload or other complications.

**Correct Answer:** D. Blood transfusion.