Which of the following units is not a unit of volume in the SI system?

In the International System of Units (SI), volume is measured in units that express three-dimensional space. Cubic meters and liters are both recognized SI units for volume.

Cubic meters specifically represent the volume of a cube with sides measuring one meter. Liters, although not technically an SI base unit, are widely accepted as a metric unit of volume, where one liter is equivalent to one cubic decimeter or (0.001) cubic meters.

On the other hand, tonnes and kilograms are units of mass, not volume. A tonne is equal to (1,000) kilograms and measures weight rather than the amount of space an object occupies. Therefore, the option that does not represent a unit of volume in the SI system is kilograms.

This distinction is important because understanding the measurements relevant to mass versus volume is crucial in fields such as engineering, where differentiating between the two can affect calculations and project planning.