In a precipitation reaction, one of the product formed is an insoluble precipitate.
The given reactions can be written with phases included as:
A. [tex]Na_{2}S(aq)+FeBr_{2}(aq)-->2NaBr(aq)+FeS(s)[/tex]: In this reaction one of the product, FeS is insoluble. Therefore, this is a precipitation reaction.
B. [tex]MgSO_{4}(aq)+CaCl_{2}(aq)-->MgCl_{2}(aq)+CaSO_{4}(s)[/tex]: In this reaction, the product [tex]CaSO_{4}[/tex]is a solid(insoluble). So, this is a precipitation reaction too.
C.[tex]LiOH(aq)+NH_{4}I(aq)-->LiI(aq)+NH_{4}OH(aq)[/tex]: In this reaction, both the products are soluble. So this is not a precipitation reaction.
D.[tex]2NaCl(aq)+K_{2}S(aq)-->Na_{2}S(aq)+2KCl(aq)[/tex]: In this reaction, both the products are soluble. So this is not a precipitation reaction.
E. [tex]AgNO_{3}(aq)+NaCl(aq)-->AgCl(s)+NaNO_{3}(aq)[/tex]: In this reaction, the product AgCl is a precipitate. So, it is a precipitation reaction.
