Which of the following should be communicated to the Flight Deck?

The appropriate communication to the Flight Deck is the location and severity of the fire. This information is critical because it directly impacts the safety of everyone on board. In the event of a fire, the Flight Deck needs detailed information to assess the situation and determine the most appropriate and immediate course of action, such as whether to prepare for an emergency landing or to initiate fire suppression procedures.

While the number of passengers on board, time of departure, and weather conditions outside are important operational details, they do not have the immediate implications for safety that the location and severity of a fire do. The primary concern during an emergency situation such as a fire is to ensure the safety of passengers and crew, making rapid and informed decisions necessary, which rely heavily on accurate and timely information about the threat posed by the fire.