What is the unit used to measure the quantity of electric charge?

The correct unit used to measure the quantity of electric charge is the Coulomb. The Coulomb is defined as the amount of charge that is transferred by a constant current of one ampere in one second. This fundamental unit is crucial in the study of electricity and is part of the International System of Units (SI). Understanding the role of the Coulomb helps to grasp concepts related to current, voltage, and electric fields, which are integral aspects of electricity and circuits.

The other choices represent different electrical quantities. A Joule is a unit of energy, representing the work done when a force is applied to move an object one meter in the direction of the force. A Volt is the unit of electric potential difference, reflecting how much energy per unit charge is available to move charge through a circuit. An Ampere, often referred to as an "amp," is the unit of electric current, signaling how much charge flows through a conductor. Each of these units serves a distinct role in the broader understanding of electric phenomena, but when specifically referring to the quantity of electric charge, the only correct answer is the Coulomb.