What instruments are required for a day VFR part 135 operation?

In day VFR (Visual Flight Rules) operations under Part 135, the required instruments are primarily those that assist in the safe navigation and operation of the aircraft. The instruments specified in the correct choice include the airspeed indicator (ASI), altimeter (ALT), compass, and turn and slip indicator.

The airspeed indicator is essential for maintaining control of the aircraft by ensuring it is operating within safe speed ranges. The altimeter provides crucial information regarding the aircraft's altitude, which is vital for traffic separation, terrain awareness, and compliance with altitude assignments. The compass is necessary for navigation, enabling pilots to maintain a desired course. The turn and slip indicator aids pilots in managing their heading during maneuvers, ensuring smooth and safe flight operations.

Other choices present instruments that may be useful for navigation and safety but are not strictly required for day VFR operations. For instance, while options concerning equipment such as radio or enhanced navigational aids are beneficial, they are not mandated for basic VFR readiness during daytime flights. Thus, the accurate assessment of required instruments clearly underscores the fundamental tools necessary for conducting a safe VFR operation under the specified regulations.