Which of the following elements is considered the best electrical conductor?

Potassium is considered the best electrical conductor among the given options because it is a metal that possesses high electrical conductivity. Metals have free-moving electrons which allow them to conduct electricity efficiently. Potassium is an alkali metal, and like other metals in this group, it has a relatively low ionization energy, enabling the easy flow of electrons. This characteristic allows potassium to allow electrical currents to pass through it with minimal resistance.

Bromine is a non-metal and is a liquid at room temperature, which generally makes it a poor conductor of electricity as non-metals tend to have localized electrons rather than free-moving ones. Arsenic is a metalloid and does not conduct electricity as well as metals, although it does have some level of conductivity. Carbon exists in multiple allotropes, like graphite and diamond; while graphite can conduct electricity due to its free electrons, it still does not surpass the conductivity of metals like potassium. Therefore, potassium's intrinsic properties as a metal make it the best conductor in this scenario.