Final answer:
Hemoglobin is the protein that changes shape and color in the presence of oxygen, due to the iron within its heme groups binding to oxygen. It is responsible for transporting oxygen to body cells and transporting carbon dioxide to the lungs, while giving blood its red color when oxygenated.
Step-by-step explanation:
The protein capable of changing shape and color in the presence of O2 is (b) Hemoglobin. Hemoglobin is a complex globular protein located in red blood cells that has a quaternary structure composed of four symmetrical subunits, each with an iron-containing heme group. The iron within the heme binds oxygen, facilitating the transport of oxygen to body cells and carrying carbon dioxide back to the lungs. The binding of oxygen to the iron within the heme group causes a change in the oxidation state of the iron and induces a conformational change in the structure of hemoglobin, which in turn alters its color, giving blood its characteristic red color when oxygenated.