Which of the following is a responsibility of the No3 during the PDIs?

The No3, or the third cabin crew member, plays a critical role during passenger service and is responsible for various safety and service-related checks, particularly in designated areas of the cabin. The responsibility to conduct cabin checks at specific rows, such as rows 12-23, aligns with ensuring that safety equipment is operational, that the cabin is orderly, and that passenger needs are being met, which is an essential aspect of their duties during pre-departure checks (PDIs).

This option emphasizes the No3's focus on maintaining high safety and service standards in the cabin, confirming that the environment is prepared for the flight and that passengers are seated correctly. The other tasks listed, such as checks at the R1 and L1 doors or G6 stowage, involve different crew responsibilities or pertain to different areas typically managed by other crew members. Each role in the cabin crew has specific duties to ensure the overall efficiency and safety of flight operations, and the No3's responsibility for cabin checks is key to fulfilling these objectives.