Answer:
when soluble ionic reactants combine to form insoluble products.
Step-by-step explanation:
Precipitation reactions are those reactions in which two soluble substances which are ionic in nature combine together forming insoluble salt. This insoluble salts is called precipitate and the reaction is called precipitation reaction. Precipitate is solid substance which is deposited at the bottom of the solution as insoluble material. This precipitate mostly formed in double replacement reaction.