Under what conditions does a precipitate form in an aqueous chemical reaction

Answer : The condition in which precipitation reaction can occur in any aqueous chemical reaction is when the cations of one reactant and the anions of other reactant reacts in aqueous solutions forms an insoluble ionic solid, which is called as "Precipitate".

It is widely known that most of precipitation reactions are formed in a double-replacement reaction. Where one element is displaced by another element of higher reactivity.

the number of valence electrons for each molecule or ion is shown beneath the structure. remember hydrogen will not have more than two electrons. this hydrogen is part of a covalent bond (sharing two electrons). a double bond here would cause hydrogen to share four electrons with phosphorus.