Here's why:

* Chemical reaction: When chlorine gas (Cl₂) dissolves in water, it reacts with water to form hypochlorous acid (HOCl) and hydrochloric acid (HCl):

Cl₂ + H₂O ⇌ HOCl + HCl

* Equilibrium: This reaction is an equilibrium reaction, meaning it goes in both directions. However, the formation of HOCl and HCl is favored, which means that some chlorine gas will always remain dissolved in water.

* Factors affecting solubility: The solubility of chlorine gas in water is affected by factors like temperature and pressure.

Important note: While chlorine gas is somewhat soluble in water, it's important to remember that it's a highly toxic gas. Handling chlorine gas requires proper safety precautions and equipment.