Coordination compounds are of great importance in biological systems. In this context,which of the following statements is incorrect?

• A
  The green color of plant leaves is due to the chlorophyll complex,which contains $Ca$ metal ion.
• B
  The red color of blood is due to the hemoglobin complex,which contains $Fe$ metal ion.
• C
  Cyanocobalamin is known as vitamin $B_{12}$,which contains a cobalt metal ion.
• D
  Carboxypeptidase-$A$ is an enzyme that contains zinc.