The coordination geometry of the active site of the zinc ion in carbonic anhydrase enzyme is a distorted tetrahedral geometry. The zinc ion is coordinated to three histidine residues His94, His96, and His119 in human carbonic anhydrase II and a water molecule or hydroxide ion.The catalytic conversion of CO2 to bicarbonate by carbonic anhydrase proceeds through the following steps:1. The zinc-bound water molecule acts as a nucleophile and attacks the CO2 molecule, which enters the active site. The presence of the zinc ion lowers the pKa of the bound water molecule, making it more nucleophilic and facilitating the attack on CO2.2. The formation of a zinc-bound bicarbonate intermediate occurs, where the CO2 molecule is now covalently attached to the oxygen of the water molecule.3. The bicarbonate ion is released from the active site, and a new water molecule binds to the zinc ion, restoring the enzyme to its original state and allowing it to participate in another catalytic cycle.The distorted tetrahedral geometry of the zinc ion in the active site plays a crucial role in this process. The zinc ion polarizes the bound water molecule, making it more nucleophilic and capable of attacking the CO2 molecule. Additionally, the geometry allows for optimal positioning of the histidine residues and the water molecule for efficient catalysis. The overall effect of the zinc ion and its coordination geometry is to lower the activation energy for the conversion of CO2 to bicarbonate, thus increasing the reaction rate significantly.