**Core Concept**
Hemoglobin is a protein in red blood cells that carries oxygen from the lungs to the body's tissues. It is composed of heme and globin, with the heme group containing iron. The iron in hemoglobin is crucial for its function in oxygen transport.

**Why the Correct Answer is Right**
One gram of hemoglobin contains approximately 3.34 milligrams of iron. This is because the heme group in hemoglobin contains a porphyrin ring with an iron ion at its center. The iron in hemoglobin is essential for the binding of oxygen to hemoglobin, and its presence is critical for the protein's function. The iron content in hemoglobin is a key factor in the diagnosis and management of conditions such as anemia.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not provide a specific amount of iron per gram of hemoglobin.
**Option B:** This option is incorrect because it does not accurately represent the amount of iron in hemoglobin.
**Option C:** This option is incorrect because it is not the correct amount of iron per gram of hemoglobin.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the iron content in hemoglobin is a key factor in the diagnosis and management of conditions such as anemia. A decrease in the iron content in hemoglobin can lead to reduced oxygen delivery to tissues, resulting in symptoms such as fatigue and shortness of breath.

**Correct Answer:** C. 3.34 milligrams.