The structure of hemoglobin consists of chains. two of the chains are and two are beta proteins. each of the protein chains are conjugated to a nonprotein group. this group contains a(n) ion in the center. there are four of these groups that will bind for delivery to body tissues.

In most mammals, hemoglobin consists of 4 distinct subunits. These subunits consist of an aminoacid chain (aminoacids are the building blocks of proteins) and a heme group. 2 of the subunits have a protein chain with a-structure and 2  have a protein chain with beta structure. The heme groups give hemoglobin and thus blood its red color. Each of these groups has a positively charged iron ion in its core. Iron is necessary so that hemoglobin can bind oxygen and transfer it through the blood flow to the tissues. Given the above exposition, the correct answers are: 4, alpha proteins, heme, iron, oxygen.
Bonus: Hemoglobin is an important example of protein structure since it shows that not only aminoacid order (secondary structure) and configuration of protein chains (tertiary structure) are crucial to the function of a protein; how the multiple chains bind to each other is equally critical (quaternary structure).