For what purpose is a temporary "1 by 1" format (letter-number-letter) call sign assigned?

The "1 by 1" call sign format is specifically reserved for special events and activities that hold significance within the amateur radio community. This format allows operators to draw attention to particular events, such as commemorative celebrations, conventions, or any activities that promote amateur radio. Using "1 by 1" call signs can enhance the visibility of these events and often attract more operators and interest from the public.

While the other options might hold relevance in different contexts, they do not specifically pertain to the purpose of the "1 by 1" call signs. For example, experimental stations have their own unique identifiers, and honoring a deceased relative could be done through other means without needing such a specific call sign format. Therefore, the correct answer emphasizes the unique application of "1 by 1" call signs in alignment with special events, setting them apart from other types of assignments in amateur radio.