Explanation: The amount of electrical energy stored in an electrostatic field is expressed in **Joules**. A Joule is the standard SI unit of energy, representing the work done or the energy expended when a force of one Newton is applied over one meter. In electrical terms, it signifies the capacity to do work, such as the energy stored in a capacitor's electrostatic field. * **B) Coulombs** are units of electric charge, not energy. One Coulomb represents the charge of approximately $6.24 \times 10^{18}$ electrons. * **C) Watts** are units of power, which is the *rate* at which energy is transferred or consumed (Joules per second). They do not measure stored energy. * **D) Volts** are units of electric potential or potential difference (electromotive force). One Volt is defined as one Joule per Coulomb, indicating the energy per unit charge, not the total energy stored.