Which of the following SI units represents the smallest quantity?

• A. centimeter (cm)
• B. millimeter (mm)
• C. micrometer (µm)
• D. nanometer (nm)

Answer: (D)

Verified step by step guidance

1. Understand that the problem is asking which unit represents the smallest length among the given options.
2. Recall the metric prefixes and their corresponding powers of ten: centimeter (cm) = 10^{-2} meters, millimeter (mm) = 10^{-3} meters, micrometer (\mu m) = 10^{-6} meters, and nanometer (nm) = 10^{-9} meters.
3. Compare the powers of ten for each unit to determine which is the smallest: the smaller the exponent, the smaller the unit.
4. Identify that nanometer (nm), being 10^{-9} meters, is smaller than micrometer (10^{-6} m), millimeter (10^{-3} m), and centimeter (10^{-2} m).
5. Conclude that nanometer (nm) represents the smallest quantity among the listed units.