What occurs periodically throughout the sortie, as required by Number 1?

During a sortie in formation flying, periodic checks on fuel and G forces are essential for the safety and tactical effectiveness of the flight. These checks, often referred to as "fuel and G checks," help ensure that each aircraft is managing their fuel levels appropriately and maintaining an acceptable G load on their airframes.

Number 1, or the lead aircraft in formation, has the responsibility for monitoring the overall formation's status, which includes ensuring every aircraft is well within safe operating parameters for fuel and G forces. This ensures that all aircraft in the formation can complete the mission effectively without risking running out of fuel or exceeding safe G limits, which could compromise performance and safety.

In contrast, the other options like takeoff procedures, formation adjustments, and landing protocols are critical phases of flight but are not conducted periodically throughout the sortie in a sustained manner like fuel and G checks. Instead, they are more tied to specific phases of flight and do not require the same level of ongoing, frequent communication and confirmation between the aircraft. Therefore, the focus on monitoring fuel and G levels periodically makes this answer the correct choice.