When potassium iodide (KI) solution is added to a lead nitrate (Pb(NO₃)₂) solution in a test tube, the compound that precipitates is lead iodide (PbI₂) .

Here's the chemical reaction:

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

Explanation:

* Lead iodide (PbI₂) is insoluble in water, so it forms a bright yellow precipitate.

* Potassium nitrate (KNO₃) is soluble in water, so it remains dissolved in the solution.

This reaction is a classic example of a double displacement reaction where the positive and negative ions of the two reactants switch partners.