Which prefix denotes 10^-3?

• A. 10^-2
• B. 10^-3
• C. 10^-9
• D. 10^3

Answer: (B)

In the metric system, prefixes express powers of ten. The prefix that denotes 10^-3 is milli-, meaning one-thousandth of a unit. That shows up in measurements like millimeter (one thousandth of a meter) or milligram (one thousandth of a gram). The other choices correspond to different powers of ten: centi- is 10^-2 (one hundredth), nano- is 10^-9 (one billionth), and kilo- is 10^3 (one thousand).