Which of the following is NOT an SI base unit?

• A. kelvin
• B. second
• C. liter
• D. kilogram

Answer: (C)

Verified step by step guidance

1. Understand what SI base units are: SI base units are the fundamental units defined by the International System of Units from which all other units are derived. Examples include meter (length), kilogram (mass), second (time), kelvin (temperature), ampere (electric current), mole (amount of substance), and candela (luminous intensity).
2. Review each option given: kelvin, second, kilogram, and liter.
3. Identify which units are SI base units: kelvin is the SI base unit for temperature, second is the SI base unit for time, and kilogram is the SI base unit for mass.
4. Recognize that liter is a unit of volume and is not an SI base unit; it is a derived unit (1 liter = 1 cubic decimeter).
5. Conclude that the unit which is NOT an SI base unit among the options is the liter.