Answer : 3. "Iron"
Explanation :

Iron is the metal found in blood. It is an essential mineral that plays a key role in transporting oxygen from the lungs to the rest of the body and carrying carbon dioxide back to the lungs to be exhaled. Iron is a crucial component of hemoglobin, a protein in red blood cells that binds to oxygen and gives blood its red color. Without sufficient iron, the body cannot produce enough healthy red blood cells, leading to iron-deficiency anemia, a common nutritional disorder.