Final answer:
Sodium carbonate (Na2CO3) is the compound that would not form a precipitate in the given options because sodium salts are typically soluble in water.
Step-by-step explanation:
In the context of precipitation reactions and solubility rules, the compound that would not be expected to form a precipitate among the options provided would be Option 4: Sodium carbonate (Na2CO3). According to the solubility rules, most sodium salts, including sodium carbonate, are soluble in water, which means they remain dissolved in solution rather than forming a solid precipitate. In contrast, silver chloride (AgCl), barium sulfate (BaSO4), and lead iodide (PbI2) are known to be insoluble under standard conditions and would therefore form precipitates when their respective ions are present in a solution.