Which of the following is not an MKS unit?

The correct answer is based on the understanding of the MKS system, which stands for Meter-Kilogram-Second. This system is a standard set of units in the International System of Units (SI). In this system, the meter is the unit of length, the kilogram is the unit of mass, and the second is the unit of time.

Centimeter, while commonly used in various contexts, is not part of the MKS system because it is a smaller unit derived from the meter (1 centimeter equals 0.01 meters). The MKS system specifically utilizes the meter as its base unit for length. Therefore, the centimeter does not qualify as an MKS unit, leading to its selection as the correct answer.

The meter, gram, and second are all clearly defined and fundamental units in the MKS system, distinguishing them from the centimeter, which is instead a subunit of the meter.