When potassium iodide (KI) and lead nitrate (Pb(NO3)2) are combined in aqueous solution, a chemical reaction takes place resulting in the formation of lead iodide (PbI2) and potassium nitrate (KNO3).

The reaction can be represented by the following chemical equation:

2KI(aq) + Pb(NO3)2(aq) → PbI2(s) + 2KNO3(aq)

In this reaction, the potassium ions (K+) and nitrate ions (NO3-) from potassium iodide and lead nitrate, respectively, remain unchanged and form potassium nitrate (KNO3). Meanwhile, the lead ions (Pb2+) from lead nitrate combine with iodide ions (I-) from potassium iodide to form lead iodide (PbI2).

Lead iodide is a bright yellow, insoluble compound that precipitates out of the solution. The precipitation of lead iodide can be observed as a cloudy or turbid appearance in the reaction mixture.

It's important to note that lead iodide is a toxic substance, and appropriate safety precautions should be taken when working with lead compounds.