What is the unit of frequency?

The "Hertz" (abbreviated Hz) is the internationally recognized standard unit of frequency. Named after the physicist Heinrich Hertz, one Hertz is defined as exactly one complete cycle per second. The other options are units for completely different electrical properties. A "Henry" measures inductance, and a "Farad" measures capacitance. "Epicycles per second" is an entirely made-up nonsense term designed to distract you.