Final answer:
The metric base unit used to record mass is the gram. The gram is defined as one-thousandth of a kilogram.
Step-by-step explanation:
In the metric system, the gram is used as the base unit to record mass. The kilogram (kg) is also a commonly used metric unit for mass. The gram is defined as one-thousandth of a kilogram. Mass is typically measured using a balance in the laboratory, which is calibrated with a standard mass to ensure accurate measurements.