Final answer:
Iron is the metal at the heart of oxygen binding in hemoglobin, which allows red blood cells to transport oxygen throughout the body.
Step-by-step explanation:
The metal responsible for oxygen binding in the hemoglobin molecule is iron (c). Hemoglobin is an integral component of red blood cells and its primary role is to transport oxygen from the lungs to the body's tissues. Each hemoglobin molecule is structured with four subunits and each contains an iron ion. These iron ions change their oxidation state in response to oxygen binding and release, facilitating the crucial process of oxygen transport throughout the body.