What type of preservative creates an invisible protective film around an item to prevent corrosion?

Volatile Corrosion Inhibitors (VCI) are designed to create an invisible protective film around metal surfaces, effectively preventing corrosion. When a VCI is applied, it volatilizes and disperses into the air within a sealed environment or packaging. As these vapors settle onto the metal surfaces, they form a very thin layer that protects against moisture and contaminants in the air, which are the primary contributors to corrosion.

This protective layer works by creating a barrier that interrupts the electrochemical reactions responsible for corrosion. It's particularly effective for items that may be stored or transported over long periods, as it helps ensure the longevity and integrity of the metal without altering its appearance or function.

The other choices serve different purposes; for example, chemical desiccants absorb moisture rather than create a barrier, active corrosion inhibitors require a ongoing presence to be effective, and passive seals primarily serve as barriers themselves rather than forming protective films. Thus, the unique ability of VCIs to provide a vapor-based protective film distinguishes them as the correct answer in this context.