Final answer:
In the redox reaction, silver (Ag) is the element that has been reduced, as it gains an electron and undergoes a decrease in oxidation state from +1 to 0.
Step-by-step explanation:
The element that has been reduced in the redox reaction AgNO₃ + Na → NaNO₃ + Ag is silver (Ag). In a redox reaction, the element that gains electrons undergoes reduction.
Here, silver ions (Ag+) gain an electron to form metallic silver (Ag), thus silver has been reduced. Since the oxidation state of silver changes from +1 in Ag+ to 0 in Ag, it clearly undergoes a decrease in oxidation number, indicating a reduction. The sodium (Na) is oxidized as it loses an electron to form sodium ions (Na+).