Step 1: Write the precipitation reaction.
When silver nitrate reacts with potassium iodide,
\[
AgNO_3 + KI \rightarrow AgI \downarrow + KNO_3
\]
A precipitate of silver iodide is formed.
Step 2: Consider the reagent present in excess.
The question states that \(KI\) is present in excess.
Therefore, after precipitation, iodide ions remain in solution.
Step 3: Determine the charge on colloidal particles.
According to the preferential adsorption theory, the ion present in excess gets adsorbed on the surface of the precipitate.
Since \(I^-\) ions are present in excess, they are adsorbed on the surface of \(AgI\) particles.
Thus, the colloidal particles become negatively charged.
The colloidal sol is represented as
\[
AgI/I^-
\]
Step 4: Final conclusion.
Hence, the colloidal solution formed is
\[
\boxed{AgI/I^-}
\]
Therefore, the correct option is (4).