**Core Concept:**
Hemoglobin is a protein found in red blood cells that carries oxygen from the lungs to the body's tissues. Mean Corpuscular Volume (MCV) is a measure of red blood cell size and is used to help diagnose anemia. Low MCV indicates microcytic anemia, while high MCV indicates macrocytic anemia. Serum iron and serum ferritin are markers of iron status, which is essential for normal red blood cell production.

**Why the Correct Answer is Right:**
The patient's Hemoglobin value is 9.8 g/dL, which is low, and MCV is 70 fL, indicating microcytic anemia. Microcytic anemia can be caused by iron deficiency, which is supported by low serum iron levels (50 µg/dL) and normal serum ferritin levels (100 ng/dL). Iron deficiency anemia is the most common type of microcytic anemia and is diagnosed when serum iron is low and ferritin is low or normal.

**Why Each Wrong Option is Incorrect:**
A. Low serum iron (50 µg/dL) and normal serum ferritin (100 ng/dL) make this option incorrect. Iron deficiency anemia is usually associated with low serum iron and low ferritin levels, not normal ferritin levels.
B. Low serum iron and normal ferritin levels (100 ng/dL) are consistent with iron deficiency anemia, making this option incorrect.
C. Low serum iron (50 µg/dL) and normal serum ferritin (100 ng/dL) are consistent with iron deficiency anemia, making this option incorrect.
D. Low serum iron (50 µg/dL) and normal ferritin (100 ng/dL) are consistent with iron deficiency anemia, making this option incorrect.

**Clinical Pearl:**
Anemia is a common condition in which red blood cells are underdeveloped or under-functioning, leading to reduced oxygen-carrying capacity in the blood. Iron deficiency anemia is the most common type of anemia and affects millions of people worldwide. Treatment includes iron supplementation and addressing the underlying cause of iron loss.