Which one of the following is a unit of electrical strength?

The correct answer is Volt. This unit measures electric potential difference, which reflects the electrical strength in a circuit. Volts indicate how much potential energy exists to move electric charges through a conductor, essentially defining the strength of the electrical pressure.

For context, Ohms measures resistance in an electrical circuit, Watt quantifies power (the rate of energy transfer), and Ampere measures the flow of electric current. While these are all integral components of electrical engineering and physics, they do not represent electrical strength as defined by voltage. Understanding the distinctions among these units is crucial for grasping how electrical systems operate.