What is the prefix for a factor of 10^-9?

The prefix for a factor of 10^-9 is "nano." In the metric system, "nano" denotes one billionth of a unit, which corresponds precisely to the factor of 10^-9. This prefix is commonly used in various scientific fields; for example, a nanometer is one billionth of a meter, often used in physics and chemistry to measure wavelengths and sizes at atomic or molecular scales.

The other prefixes listed—pico, femto, and deci—represent different factors: pico is 10^-12, femto is 10^-15, and deci is 10^-1. Each of these prefixes signifies a distinct magnitude of measurement, making "nano" the accurate designation for a factor of 10^-9. Understanding these prefixes is crucial for interpreting scientific data accurately and for communicating measurements in a standardized way.