Which of the following SI units is the smallest?

• A. micrometer
• B. nanometer
• C. centimeter
• D. millimeter

Answer: (B)

Verified step by step guidance

1. Step 1: Understand the prefixes used in the SI units. Each prefix represents a power of ten that scales the base unit (meter in this case). For example, 'micro-' means 10^{-6}, 'nano-' means 10^{-9}, 'centi-' means 10^{-2}, and 'milli-' means 10^{-3}.
2. Step 2: Convert each unit to meters using their respective prefixes: \\micro meter = 1 \\times 10^{-6} meters, nanometer = 1 \\times 10^{-9} meters, centimeter = 1 \\times 10^{-2} meters, millimeter = 1 \\times 10^{-3} meters.
3. Step 3: Compare the numerical values of each unit in meters to determine which is the smallest. The smaller the exponent (more negative), the smaller the unit.
4. Step 4: Identify the unit with the smallest value in meters, which corresponds to the smallest length among the options.
5. Step 5: Conclude that the nanometer, being 1 \\times 10^{-9} meters, is the smallest unit among the given options.