Which balanced chemical equation best represents the thermal decomposition of sodium bicarbonate? NaHCO3 (s) → NaOH (s) + CO2 (g) 2NaHCO3 (s) → Na2CO3 (s) + CO2 (g) + H2O (g)
2NaHCO3 (s) → Na2O (s) + 2CO2 (g) + H2O (g) NaHCO3 (s) → NaH (s) + CO (g) + O2 (g)

As you can see from the calculations, 2NaHCO3(s) → Na2CO3(s) + CO2(g) + H2O(g) was the reaction that happened when heating the NaHCO3 because its theoretical mass from the equation is almost exactly the same as the actual mass of the product from the experiment.

the answer is na (sodium)