After receiving NITS from the Captain, what must N2 do immediately?

Upon receiving NITS from the Captain, N2 must immediately repeat the information to N1. This process ensures that all essential safety information is accurately communicated and confirms that N1 is fully aware of the situation. Effective communication among crew members is critical, especially in emergency scenarios, to ensure that all actions taken are coordinated and that everyone is on the same page regarding the necessary procedures and responses.

Repeating the NITS (which stands for "Nature of the Emergency," "Intentions," "Time available," and "Special Instructions") serves as a confirmation step, reducing the risk of misunderstanding or miscommunication. This step is fundamental in the airline industry's safety protocols, aligning with the standard operating procedures required during emergency situations.

In the context of the other choices, checking cabin conditions, preparing evacuation slides, and informing passengers are important actions that may need to be taken, but they follow the essential confirmation of information between crew members. Therefore, repeating to N1 is the correct immediate action to ensure effective communication and readiness to handle the situation appropriately.