What is the unit of mass in the SI system?

The unit of mass in the International System of Units (SI) is the kilogram. The kilogram is defined as the mass of a specific physical prototype kept at the International Bureau of Weights and Measures. It serves as a fundamental unit of measurement for mass, and it is used globally in scientific research, engineering, and everyday commerce.

While grams are also used as a unit of mass, they are derived from the kilogram, where 1 kilogram equals 1,000 grams. The other choices, such as meter and second, represent different fundamental quantities: meter is the unit of length, and second is the unit of time. Therefore, the correct answer reflects the SI system's standard unit specifically for measuring mass.