Which prefix represents one-thousandth (10⁻³)?

The prefix that represents one-thousandth (10⁻³) is indeed Milli. In the metric system, the prefix "milli" indicates a factor of (10^{-3}), or 0.001. This means that one millimeter is one-thousandth of a meter, one milliliter is one-thousandth of a liter, and so forth. Understanding these prefixes is essential for working with measurements in various scientific contexts, including chemistry.

In contrast, the prefix "micro" denotes one-millionth (10⁻⁶), "centi" refers to one-hundredth (10⁻²), and "deci" corresponds to one-tenth (10⁻¹). Each of these prefixes helps convey specific orders of magnitude, which is crucial in scientific communication and calculations. Therefore, the correct representation of one-thousandth in the metric system is given by the prefix milli.