Final answer:
When the magnitude of an unbalanced force applied to a crate is doubled, the inertia of the crate remains unchanged.
Step-by-step explanation:
When the magnitude of an unbalanced force applied to a crate is doubled, the inertia of the crate remains unchanged. Inertia is the resistance of an object to change its state of motion, and it is directly proportional to the mass of the object. In this case, the mass of the crate is given as 4.0 kilograms, so its inertia remains the same even if the force applied to it is doubled.