<span>Inertia is defined as "the tendency for a body to resist acceleration; the tendency of a body at rest to remain at rest or of a body in motion to stay in motion in a straight line unless disturbed by an external force" Therefore, both will have the same inertia since they have the same mass.</span>
The inertia of a body is defined as its property to oppose the state of rest or uniform motion. In this question, we have to write out of four kilograms of iron and four kilograms of cork which will have maximum inertia. Inertia of a body is also equal to measure of its mass.
In this case, the masses of both iron and cork are same i.e. 4 kg. So, it is clear that the inertia of both iron and cork are same due to their same masses.