Explanation: A capacitor is the device used to store electrical energy in an electrostatic field. It consists of two conductive plates separated by an insulating material called a dielectric. When a voltage is applied across the plates, an electric charge builds up on them, creating an electrostatic field within the dielectric, which stores the energy. This ability to store and release charge makes capacitors essential components in filters, timing circuits, and resonant circuits in radio frequency applications. A battery (A) stores energy chemically and converts it to electrical energy. A transformer (B) transfers AC energy between circuits via electromagnetic induction. An inductor (D) stores energy in a *magnetic* field when current flows through it.