In the combustion of methane molecular oxygen is the oxidizing agent and methane is the reducing agent.
In the free radical halogenation of methane molecular bromine is the oxidizing agent and methane is the reducing agent.
In the rusting of iron, molecular oxygen is the oxidizing agent and iron is the reducing agent.
In the reaction of sodium borohydride with acetone, sodium borohydride (or hydride ion) is the reducing agent and acetone is the oxidizing agent.
In the catalytic hydrogenation of propene, molecular hydrogen is the reducing agent and propene is the oxidizing agent.