Which of the following units is not part of the SI system?

The pound is not part of the SI (International System of Units) system. The SI system is an internationally accepted standard for measurement that includes predefined units to ensure consistency and clarity in scientific and engineering contexts. The key units of the SI system include the kilogram for mass, the second for time, and the metre for length.

The kilogram represents mass, the second measures time, and the metre is used for length, making them all fundamental components of the SI system. In contrast, the pound is part of the Imperial system, which is commonly used in countries like the United States for weight measurement rather than the metric system used globally, which relies on the SI units. This distinction is essential for understanding measurements in various scientific and engineering applications, where consistency in units is crucial.