Chemistry is the study of the structure and behavior of matter. It allows scientists to ask and answer questions about how the natural world works in order to solve problems. Measurements in chemistry must be reported accurately without ambiguity using standardized measurement systems and units. The International System of Units (SI) is the modern metric system that defines base units for common physical properties including the kilogram (mass), meter (length), second (time), kelvin (temperature), and liter (volume).