The base unit of mass density in the SI system is?

The base unit of mass density in the SI system is kg/m³. Mass density is defined as mass per unit volume. In the International System of Units (SI), the unit of mass is the kilogram (kg), and the unit of volume is the cubic meter (m³). Therefore, when we express mass density, we take the mass in kilograms and divide it by the volume in cubic meters, leading to the unit kg/m³.

This unit reflects how much mass is contained in a given volume and is crucial in various applications, such as calculating buoyancy, material strength, and thermal properties, among others. The other options presented do not accurately represent the SI unit for density. kg/m² represents a surface density, g/m³ is a non-standard unit for mass density as it uses grams instead of kilograms, and N/m³ is a unit of pressure or stress, not mass density.