Which of the following best describes the function of a capacitor?

A capacitor is an electronic component that primarily serves the function of storing electrical energy in an electrostatic field. When a capacitor is connected to a circuit, it accumulates charge on its plates when voltage is applied. This ability to store and release energy makes capacitors essential for various applications, such as smoothing out voltage fluctuations in power supplies, filtering signals in radio communications, and timing applications in circuits.

The other options do not accurately describe the primary function of a capacitor. While some components in an electrical system can produce voltage, increase resistance, or measure current, these functions are associated with different types of electrical components like batteries, resistors, and ammeters, respectively. Therefore, the defining characteristic of a capacitor is its role in energy storage, which is the reason why the first choice is the best answer.