Here's why:

* Molecular structure: CO2 is a linear molecule with a polar character due to the electronegativity difference between carbon and oxygen. This polarity allows it to interact more effectively with water molecules, which are also polar.

* Intermolecular forces: CO2 can form weak hydrogen bonds with water molecules, while O2, being non-polar, relies only on weaker van der Waals forces.

* Henry's Law: This law states that the solubility of a gas in a liquid is directly proportional to the partial pressure of the gas above the liquid. While both CO2 and O2 obey this law, the proportionality constant (Henry's law constant) is higher for CO2, indicating higher solubility.

Practical Implications:

* Carbonation: The higher solubility of CO2 in water is what makes carbonated beverages possible.

* Ocean Acidification: As CO2 levels in the atmosphere increase, the oceans absorb more of it, leading to a decrease in pH (acidification).

Therefore, even though both CO2 and O2 are essential gases, CO2 has a significantly higher solubility in water due to its molecular structure and interactions.