According to SI units, what is the unit of mass?

The unit of mass in the International System of Units (SI) is the kilogram. This system is widely adopted in scientific contexts and is based on a coherent set of units where the kilogram is the base unit for mass.

The kilogram is defined as the mass of a specific physical prototype kept at the International Bureau of Weights and Measures. It is important to note that the SI system has been established to provide a uniform measurement system that is used globally in scientific research and industry.

While grams are commonly used in everyday applications and are a subunit of the kilogram (1 kilogram equals 1,000 grams), they are not recognized as the base unit. Other options like pounds and ounces are units of mass used primarily in the imperial system, which is not part of the SI units. Thus, the correct choice of the unit of mass according to SI units is the kilogram.