What are the units of electrical resistance?

The units of electrical resistance are ohms. This is based on Ohm's Law, which states that the current through a conductor between two points is directly proportional to the voltage across the two points and inversely proportional to the resistance. The ohm is defined as the resistance across which a current of one ampere flows when there is a voltage of one volt across it.

Understanding this concept helps clarify why ohms are the standard unit for measuring resistance in electrical circuits. Other options represent different electrical concepts; siemens and mhos are units of conductance, which is the inverse of resistance. Coulombs are units of electric charge, not resistance. Thus, recognizing that ohms directly measure how much a material opposes the flow of electric current confirms the correct answer.