What is the reducing agent in the reaction #Fe + AgNO_3 -> Fe(NO_3)_3 + Ag#?
The reducing agent is the species that SUPPLIES the electrons, and is necessarily OXIDIZED in the process.
The stoichiometric reaction:
Since iron is oxidized, it loses electrons, the which reduce the silver ion to silver metal. So iron is the reducing agent, which becomes oxidized in the reduction of