What is the prefix that denotes 1 billionth of the standard unit in the metric system?

The prefix that signifies 1 billionth of a standard unit in the metric system is "nano." In the International System of Units (SI), "nano" is defined as a factor of 10^-9, which means it represents one part in one billion. This prefix is commonly used in various fields, particularly in nanotechnology and molecular biology, where measurements often require expressing very small quantities.

The other prefixes mentioned serve different functions: "milli" refers to one-thousandth (10^-3), "micro" denotes one-millionth (10^-6), and "giga" indicates one billion (10^9). Understanding these prefixes helps in comprehending the scale of different measurements and the relationship between them in scientific contexts.