What type of instruments requires shorter sterilization times compared to packaged instruments?

The correct answer is unpackaged instruments. Unpackaged instruments typically require shorter sterilization times because they are exposed directly to the sterilizing agent, such as steam, ethylene oxide, or other sterilants, without any barriers. This direct exposure allows for more efficient penetration and contact of the sterilizing agent, ensuring that all surfaces of the instruments are effectively sterilized in a shorter timeframe.

In contrast, the presence of packaging for instruments can create additional barriers that slow down the sterilization process. Packaged instruments might require longer exposure times to ensure that the sterilization agent can penetrate the packaging and reach all surfaces of the instruments.

Chemically treated instruments, plastic instruments, and wooden instruments have specific considerations that may affect their sterilization requirements, but they do not inherently correlate to shorter sterilization times compared to unpackaged instruments. Therefore, unpackaged instruments stand out as the correct answer in the context of this question.