Final answer:
In the chemical reaction 2NaHSO3(s) -> Na2SO3 (s) + SO2(g) + H2O(l), sodium bisulfite (NaHSO3) is the reducing agent.
Step-by-step explanation:
In the chemical reaction 2NaHSO3(s) -> Na2SO3 (s) + SO2(g) + H2O(l), sodium bisulfite (NaHSO3) is the reducing agent. The reducing agent is the substance that causes another substance to be reduced by providing electrons. In this case, sodium bisulfite is oxidized and donates electrons to another substance, leading to its reduction.