In a hemoglobin molecule, what element is central to all the structures

Iron. It is at the center of the structure. And because they'll delete my answer if I don't add on: Hemoglobin is the oxygen binding protein of red blood cells and is a globular protein with quaternary structure. Hemoglobin consists of four polypeptide subunits; 2 alpha chains and two beta chains. Hemoglobin transports oxygen in the blood from the lungs to the rest of the body.

the correct answer is b. a strong acid completely dissociates to its ions when dissolved in water. completely dissociates to and ions. a is incorrect because does not fully ionize to and ions and some remain as the compound . c and d are incorrect because, and do not fall into the category of bronsted lowry acids. a bronsted lowry acid is a proton donor and since both molecules do not have a proton to donate they are not bronsted lowry acids. likewise,   if we use the lewis acid definition, they cannot be acids. a lewis acid is an electron pair acceptor. both and have a complete octet so can not accept any electrons which disqualifies them as acids.