Balance and state of the reactions are precipitation, acid/base, or oxidation/reduction reactions.

A) Fe + O2 -> Fe2O3

B) Br2 + Fe(NO3)2 + KNO3 -> KBr + Fe(NO3)3

C) Ba(OH)2 + HNO3 -> H2O + Ba(NO3)2

D) NaF + Mg(NO3)2 -> MgF + NaNO3