1) We need to find out every molecule.
Reactants
Baking soda: NaHCO3
Citric acid: C6H8O7
Water: H2O
Possible products
Sodium citrate: Na3C6H5O7
Sodium nitrate: NaNO3
Ammonium nitrate: NH4NO3
2) Set the chemical equation (reactants)
3) According to the reactants we can expect in the products' side elements such as Sodium, Carbon, Hydrogen, and Oxygen. So, those compounds with Nitrogen cannot be in the reaction.