**Core Concept**
Normal reduced hemoglobin in blood is a critical parameter in hematology, reflecting the amount of functional hemoglobin available for oxygen transport. Reduced hemoglobin is typically measured in terms of the hemoglobin concentration in grams per deciliter (g/dL). This value is essential for diagnosing and managing various anemia-related conditions.

**Why the Correct Answer is Right**
The correct answer is determined by the World Health Organization's (WHO) standard reference value for hemoglobin concentration in adults, which is approximately 13.5-17.5 g/dL for adult men and 12-16 g/dL for adult women. A hemoglobin concentration below these values may indicate anemia. The normal reduced hemoglobin value is crucial for assessing the severity of anemia and guiding treatment decisions. In clinical practice, healthcare professionals often use laboratory tests, such as the complete blood count (CBC), to measure hemoglobin levels and diagnose anemia.

**Why Each Wrong Option is Incorrect**
**Option A:** This value is too high for normal reduced hemoglobin in adults.

**Option B:** This value is too low for normal reduced hemoglobin in adults.

**Option C:** This value is within the normal range but may not be the most accurate reference value for adult populations.

**Clinical Pearl / High-Yield Fact**
It's essential to note that hemoglobin concentration can be affected by various factors, including age, sex, altitude, and nutritional status. Therefore, healthcare professionals should consider these factors when interpreting hemoglobin values in individual patients.

**Correct Answer:** D.