Answer: The species oxidized is
.
The species reduced is

The oxidizing agent is

The reducing agent is

Step-by-step explanation:
Oxidation reaction is defined as the reaction in which a substance looses its electrons. The oxidation state of the substance increases.
Reduction reaction is defined as the reaction in which a substance gains electrons. The oxidation state of the substance gets reduced.

On reactant side:
Oxidation state of mercury = +2
Oxidation state of iodine = -1
On product side:
Oxidation state of mercury = 0
Oxidation state of iodine = 0
The oxidation state of mercury reduces from +2 to 0, it is getting reduced. Thus, it is getting reduced and acts as oxidizing agent.
The oxidation state of iodine increases from -1 to 0. Thus, it is getting oxidized and acts as reducing agent .