The California agency disclosure form is required in a transaction involving:

The California agency disclosure form is a crucial document that ensures all parties in a real estate transaction are aware of who represents whom, and it clarifies the duties and obligations of the agents involved. The correct option indicates that this form is specifically required when dealing with manufactured or mobile homes that are not attached to land.

This requirement ensures that buyers and sellers are well-informed about the relationship and responsibilities of the agents representing them in these specific types of transactions. Manufactured or mobile homes present unique characteristics and legal considerations, particularly when they are not affixed to real property. As such, the agency disclosure form plays a vital role in maintaining transparency and protecting the interests of the parties involved.

In contrast, the other scenarios described—sales of duplex units, business opportunities, and commercial properties—have different regulatory requirements and may not specifically mandate the agency disclosure form in the same manner or under the same circumstances as detached manufactured or mobile homes. Each type of transaction may follow distinct guidelines based on state laws, market practices, and the nature of the properties involved, highlighting why the requirement applies primarily to the situation specified in the correct answer.