Answer:
Cl⁻ is the reducing agent.
Step-by-step explanation:
In any complete redox reaction there is one species which gets oxidized (by giving electrons) and another reduced (by accepting electrons)
During oxidation the chemical species undergoes an increase in oxidation number.
During reduction the chemical species undergoes a decrease in oxidation number.
The reagent which undergoes oxidation acts as reducing agent and the one which undergoes reduction acts as oxidizing agent.
So here in the given problem, MnO₂ undergoes reduction and Cl- undergoes oxidation hence Cl- is the reducing agent.