Concept:A capacitor is a device that stores electric charge by maintaining an electric field between two conductors.
Explanation:A transformer only transfers electrical energy between circuits, so it does not store charge.
An ammeter measures the amount of electric current flowing in a circuit.
A potentiometer is used to measure or compare potential differences.
A capacitor, on the other hand, stores electric charges by collecting positive charge on one plate and negative charge on the other plate, which are separated by an insulating material.
This stored charge can be released when needed by the circuit.
Hence, the device used for storing electric charges is the capacitor.
Answer:D. Capacitor