Porphyrin complexes are among the most important chelating agents in nature. Which statement is correct concerning these?
(a) Hemoglobin can bind up to two O2 molecules.
(b) Myoglobin is a protein that contains four heme groups.
(c) Heme is a porphyrin in which the metal ion is Fe(II).
(d) Chlorophylls are porphyrins that contain Ca(II).