Which regulation specifies instrument range markings for airplanes in the normal category?

The regulation that specifies instrument range markings for airplanes in the normal category is indeed Part 23. This part of the Federal Aviation Regulations (FAR) defines the airworthiness standards for airplanes, particularly those with a maximum seating capacity of 19 passengers or a maximum payload capacity of 6,000 pounds, designed for non-commercial operations. Within Part 23, there are specific requirements addressing the design and specification of instrument marking to ensure clarity and usability for pilots.

This regulation helps maintain safety and operational standards by ensuring that pilots can quickly and accurately interpret the information presented by their instruments, which is critical for the safe operation of aircraft. It includes guidance on the layout, visibility, and accuracy expectations for the markings, which facilitate proper pilot response under various flying conditions.

Other parts mentioned, such as Part 25, Part 29, and Part 35, focus on different aircraft categories and specifications, including transport category airplanes and rotorcraft, but they do not pertain specifically to the normal category of airplanes. This context reinforces why Part 23 is the correct choice regarding instrument range markings for normal category aircraft.