What is the unit of power in the SI system?

The SI unit of power is the Watt. Power in physics is defined as the rate at which work is done or energy is transferred over time. One Watt is equivalent to one Joule per second, indicating that if one Joule of energy is used in one second, the power is one Watt. This quantifies how quickly energy is being converted or used, which is essential in various applications, particularly in engineering and electrical systems.

Other options represent different physical quantities: Pascal is the unit of pressure, Newton-metre (also known as Joule) is a unit of torque or energy depending on context, and Joule is the unit of energy. Thus, while they are all important in their respective fields, only the Watt specifically refers to power.