Which of the following SI units is most appropriate for identifying an unknown substance based on its mass?

• A. kilogram (kg)
• B. second (s)
• C. ampere (A)
• D. meter (m)

Answer: (A)

Verified step by step guidance

1. Understand that the problem asks for the SI unit most appropriate for identifying an unknown substance based on its mass.
2. Recall that mass is a measure of the amount of matter in an object, and the SI unit for mass is the kilogram (kg).
3. Recognize that the other units given—second (s), ampere (A), and meter (m)—represent time, electric current, and length respectively, which are not related to mass.
4. Conclude that since mass is the property used to identify the substance, the kilogram (kg) is the correct and most appropriate SI unit.
5. Therefore, the kilogram (kg) is the best choice for identifying an unknown substance based on its mass.