The correct answer to the question is A) Electrons.
EXPLANATION:
The electrical conductivity of a metal or any substance depends on the free electron concentration of the metals.
Free electrons are those electrons which are present in the conduction band of the metals. These electrons experience less amount of force attraction from the nucleus. Protons and neutrons do not contribute anything to the current conduction in a metal.These sub atomic particles are bound to the nuclei of atoms.
When we maintain potential difference across the two ends of a conductor, the free electrons are drifted towards the positive terminal of the battery.
Hence, electrical conductivity of a substance is the ability of the electrons to move inside the substance.
More is the conductivity of the substance, the lesser is the resistance to the flow of electrons inside the substance, and vice versa.
