The correct option is A Cu++
Hemocyanin is oxygen carrier of many molluscs and arthropods contains two Cu++ ions in its active site. These are suspended directly in the hemolymph. On oxidation, during the gaseous stage, the copper ions change its colour from clear to blue. Copper ions are complexed by three histidine residues that form the distorted pyramidal geometry of each atom. The space between the copper atoms facilitates the bonding of the two copper atoms to each dioxygen molecule. So, the correct answer is option A.