To balance the given unbalanced chemical equation:
\[ 2 \text{NaHCO}_3 \rightarrow \text{Na}_2\text{CO}_3 + \text{CO}_2 \]
We start with 2 sodium (Na), 2 carbon (C), 6 oxygen (O), and 2 hydrogen (H) atoms on the reactant side. The products consist of 2 sodium (Na), 1 carbon (C) in Na2CO3, and 2 carbon (C) in CO2, totaling 3 carbon, and there are 3 oxygen in Na2CO3 plus 2 oxygen in CO2 (5 oxygen in total).
To balance the hydrogen, we need more molecules in the products.
The equation does not appear to be balanced for hydrogen. The missing hydrogen atoms can be balanced by adding water (H2O) on the product side.
Therefore, adding water (H2O) helps balance the equation:
Final balanced equation:
\[ 2 \text{NaHCO}_3 \rightarrow \text{Na}_2\text{CO}_3 + \text{CO}_2 + \text{H}_2\text{O} \]
Thus, among the options you provided, H2O is the appropriate choice to add to the products to help balance the equation.