According to FAA regulations, which of the following is a required instrument for IFR flight?

The magnetic compass is considered a required instrument for IFR flight according to FAA regulations because it serves as a fundamental navigational aid. A magnetic compass provides pilots with heading information, which is essential for maintaining course over the ground. It is one of the basic navigational instruments that must be functional for safe instrument flight operations.

In contrast, while the vertical speed indicator, weather radar, and flight management systems are useful tools for enhancing situational awareness and managing flight operations, they are not explicitly required by FAA regulations for IFR flight. The instruments required are defined to ensure that pilots have the necessary information to navigate safely and effectively in low visibility conditions, and the magnetic compass meets that critical need.