Final answer:
In the reaction between tin (Sn) and nitric acid (HNO3), tin acts as the reducing agent because it gets oxidized from an oxidation state of 0 to +4 in tin dioxide (SnO2).
Step-by-step explanation:
In the given chemical reaction, tin (Sn) is reacting with nitric acid (HNO3) to form tin dioxide (SnO2), nitrogen dioxide (NO2), and water (H2O). To determine the reducing agent, we need to look at the oxidation states of the elements involved and identify which species is being oxidized.
Tin starts as a solid metal, Sn(s), which means it has an initial oxidation state of 0. In the product tin dioxide (SnO2), the oxidation state of tin is +4. Therefore, tin increases its oxidation state from 0 to +4, meaning it loses electrons and is therefore oxidized. Since oxidized substances are reducing agents, we can conclude that in this reaction, tin (Sn) is the reducing agent because it donates electrons to another species (in this case, to the nitric acid which is being reduced).