Final answer:
Ethane (C2H6) is the reducing agent in the balanced redox reaction 2 C2H6(g) + 7 O2(g) → 4 CO2(g) + 6 H2O(g), as it undergoes oxidation, evidenced by an increase in oxidation state from -3 to +4.
Step-by-step explanation:
In the balanced redox reaction 2 C2H6(g) + 7 O2(g) → 4 CO2(g) + 6 H2O(g), the species that serves as the reducing agent is ethane (C2H6). To identify the reducing agent, we look at the oxidation state changes for the elements involved in the reaction. Ethane goes from an oxidation state of -3 (for each carbon atom) to an oxidation state of +4 in carbon dioxide (CO2). This increase in oxidation state indicates that ethane is being oxidized and therefore serves as the reducing agent which gets oxidized itself to reduce the other species. On the other hand, oxygen (O2) is being reduced as its oxidation state decreases from 0 in molecular oxygen to -2 in water (H2O), making it the oxidizing agent.
By using the changes in oxidation numbers, we have determined that ethane (C2H6) is the reducing agent, since it donates electrons to oxygen during the combustion process.