Hb (hemoglobin) is a chromo-protein and is found exclusively in erythrocytes & myoglobin. It is red coloring pigment of blood. Hb is a is a globular protein composed of heme as prosthetic group & globin as apo-protein. Heme is iron-porphyrin complex and iron is present in heme in ferrous form (Fe2+).
Thus iron (Fe2+) is metal part of Hb.