Step 1: Understanding the Concept:
Iodine is soluble in KI solution due to complex formation.
Step 2: Detailed Explanation:
I\(_2\) reacts with I\(^-\) from KI to form the triiodide ion: I\(_2\) + I\(^-\) → I\(_3^-\). This complex is soluble in water.
Step 3: Final Answer:
\(\mathrm{I}_3^-\)