Which of the following is the unit of frequency, defined as one cycle per second?

The unit of frequency is defined as the number of cycles that occur in one second, and this is measured in Hertz. One Hertz represents one cycle per second, making it a fundamental unit in physics for quantifying periodic events, such as waves or oscillations.

In this context, Hertz is important because it provides a standardized way to discuss and measure frequencies in various scientific applications, including sound waves, electromagnetic waves, and electrical currents.

Other units mentioned, like Bel and Decibel, are related to sound intensity and logarithmic measures of power, while Newton is a unit of force. Therefore, these do not represent frequency and are not appropriate choices for defining cycles per second. Hertz is the correct and widely accepted unit for measuring frequency in physics.