What is the SI unit for mass?

The SI (International System of Units) unit for mass is the kilogram, represented as "kg." This unit is a fundamental measure in the metric system and is used universally in scientific and engineering contexts to quantify the amount of matter in an object. The kilogram is defined based on a physical object, the International Prototype of the Kilogram, which is a cylinder made of platinum and iridium, keeping its mass constant for standard reference.

Understanding why "kg" is the correct answer can also be enhanced by considering the other options. For instance, "m/s²" is a unit of acceleration, specifically the rate of change of velocity per unit time. "m" denotes meters, which are units of length, and "N" represents newtons, which are units of force. Each of these units measures different physical properties, but only "kg" specifically refers to mass. Thus, recognizing the definition and applications of the kilogram underscores its role as the standard unit for mass in scientific practices.