Okay, let's tackle this question. The question is asking at what stage of erythropoiesis hemoglobin first appears. I need to recall the stages of red blood cell development.

First, I remember that erythropoiesis starts with the hematopoietic stem cell. Then, it goes through several stages: proerythroblast, basophilic erythroblast, polychromatophilic erythroblast, orthochromatic erythroblast, and finally reticulocyte and mature RBC.

Hemoglobin synthesis is a key part here. I think hemoglobin starts being produced when the cell starts losing its nucleus. The basophilic erythroblast is where RNA is active, so maybe hemoglobin appears here. Wait, but the orthochromatic erythroblast is when the cell is losing the nucleus and hemoglobin becomes more prominent. Or is it during the polychromatophilic stage? Hmm.

Wait, in the basophilic stage, the cell is actively synthesizing hemoglobin. The cytoplasm is basophilic due to high RNA content. Then, as it matures, the cytoplasm becomes polychromatophilic (mix of basophilic and acidophilic) because hemoglobin starts accumulating. So hemoglobin is first synthesized in the basophilic erythroblast.

The correct answer is probably the basophilic erythroblast stage. Let me check. Yes, hemoglobin synthesis begins in the basophilic erythroblast. The proerythroblast is the earliest stage, but hemoglobin isn't present there. So the answer is B (assuming the options are in order). But need to make sure the options are labeled correctly. The question's options are A, B, C, D, but the correct answer is given as [Letter]. So if the correct answer is B, then the explanation should reflect that.

**Core Concept**
Erythropoiesis involves sequential maturation of erythroid precursors, with hemoglobin synthesis initiating at a specific developmental stage. Hemoglobin appears when the cell transitions from a proerythroblast to a basophilic erythroblast, reflecting active globin chain production and heme synthesis.

**Why the Correct Answer is Right**
Hemoglobin first appears in the **basophilic erythroblast** (Stage II of erythropoiesis). This stage is characterized by abundant ribosomal RNA (hence basophilic cytoplasm) and active synthesis of α- and β-globin chains, which combine with heme to form hemoglobin. The cytoplasmic basophilia gradually decreases as hemoglobin accumulates in later stages (polychromatophilic and orthochromatic erythroblasts).

**Why Each Wrong Option is Incorrect**
**Option A:** Proerythroblast (Stage I) lacks hemoglobin synthesis; it is the earliest precursor with a large nucleus and scant cytoplasm.
**Option C:** Polychromatophilic erythroblast (Stage III) contains hemoglobin but is not the *first* stage of synthesis.
**Option D:** Orthochromatic erythroblast (Stage IV) has mature hemoglobin levels but is later in the sequence.

**Clinical Pearl / High-Yield Fact**
Remember the acronym **"BAPHO"** for erythroblast stages: **B**asophilic → **

✓ Correct Answer: B. Intermedate normoblast