In the most fundamental form, electrical current is the movement of electric charge. Ampere (A) is considered to be the internationally accepted unit of electric current, and one ampere is that quantity of current as one coulomb of charge flows through a given conductor in unit time or one second. Metal wires are thought to be the strongest conductors of electric charge. Complete step by step answer: We must first understand the concept of electricity or electric current in order to understand what it is constituted by in a metal wire.We will generate the energy called as electricity or electric current if we can release an electron from an atom and cause it to travel through a medium.The movement of charge is the concept of electricity. The charges are typically brought about by electrons that can travel freely. Metal wires are basically conductors that can allow current to pass through it easily.Conductive substances are made up of atoms that have negatively charged electrons that are held on loosely. Since any electron in an atom bears a negative charge, electrons of atoms will serve as our charge carriers. The carrying of charge produces electric current across metal wires. Now let us observe all the options and understand which option could be the possible right answer. The option A electrons is the correct option. We know that the current's basic constituent is charge and that charge must be negative. The electrons are those negative charges which are responsible for current across metal conductors like wires. Then option B protons is an incorrect option, since this is another type of charge but they are positive. Electric current is only made up of negative charges hence it cannot be protons due to their positive nature. Also option C atoms is an incorrect option, since they do not constitute current. Atoms are composed of charged particles like electrons and protons. Current is constituted by charges so since atoms contain charges within them, atoms are not the constituent particles of current in any conductor. Finally option D molecules is an incorrect option, they are not exactly part of electricity. Molecules by definition are composed of multiple. Molecules are not charges but they contain charges in them because they are made up of atoms, but we know that current is a composition of charge, so molecules cannot be constituents of current. Therefore the correct answer is option A. Note:The opposite of conductors are insulators, so insulators are those objects that prevent electricity from freely flowing from one particle of that object to another. If we apply a charge to any part of such an object, the charge persists at the applied position and will not spread over the object's surface due to its property of insulation.