Because iodine is the least soluble of the three halogen elements that are soluble in water. But because of the seven f's that are available on the fourth floor. These orbitals can be used to hold other atoms, ions, or groups of atoms that can provide electrons for iodine. And it turns out that the iodine atom is the donor that provides the electron for the iodine. Each atom of iodine can provide an electron for an iodide anion. Each anion of iodine
can accept two electrons from two iodine atoms. It forms an I3- radical. This group, like many anions or acid roots, is soluble in water, so indirectly increasing the solubility of iodine in water.