What is the standard unit of mass in the metric system?

The standard unit of mass in the metric system is the kilogram. The kilogram is defined as the mass of a specific platinum-iridium cylinder kept at the International Bureau of Weights and Measures. It serves as the base unit of mass in the International System of Units (SI), which is the modern metric system used globally. In scientific contexts, the kilogram is widely used due to its convenience for measuring larger masses, which is essential in various disciplines like chemistry and physics.

The gram, while also a unit of mass in the metric system, is derived from the kilogram (1 kilogram equals 1000 grams) and is commonly used for smaller measurements. The pound and ounce, on the other hand, are units of mass in the imperial system, which is not part of the metric system. Therefore, the correct choice is the kilogram as it represents the fundamental unit within the metric framework.