Which metric prefix represents one-millionth of the base unit?

The correct choice represents the metric prefix "micro," which indicates one-millionth (or 10^-6) of a base unit. In the metric system, prefixes are used to denote specific multiples or fractions of base units, facilitating easier understanding and communication of measurements.

"Micro" is commonly seen in various scientific measurements, such as micrometers (μm) and microseconds (μs), making it an important prefix in disciplines such as biology and engineering. Each of the other prefixes listed corresponds to different values: "kilo" signifies one thousand times the base unit, "centi" represents one-hundredth, and "deca" indicates ten times the base unit. Understanding these prefixes and their associated values is essential for proper measurement and communication in scientific and medical settings.