Which combination will produce a precipitate? agno3 (aq) and ca (c2h3o2) 2 (aq) naoh (aq) and hcl (aq) nacl (aq) and hc2h3o2 (aq) nh4oh (aq) and hcl (aq) fe (no3) 2 (aq) and koh (aq) ?

The combination that will produce a precipitate is Fe (NO₃) ₂ (aq) and KOH (aq). The balanced chemical equation shows the production of iron (II) oxide, Fe (OH) ₂ (s) and potassium nitrate, KNO₃.

Fe (NO₃) ₂ (aq) + 2KOH (aq) → Fe (OH) ₂ (s) + 2KNO₃ (aq)

Fe (OH) ₂ is insoluble in water. It is naturally a white solid but in the presence of even a small amount of oxygen, it turns into a green color. That is why, it is also referred to as "green rust". The other product KNO₃ is an ionic salt that forms an aqueous solution in water.

Other combinations among the choices do not produce a solid. This is based on the solubility rules wherein it is stated that:

1. All compounds of C₂H₃O₂, Na⁺, NH₄⁺ along with other alkali metals are soluble in water.

2. All compounds with Cl are soluble except for Pb, Hg, and Ag.