Which is equal to one microvolt?

One microvolt is defined as one millionth of a volt. This is represented mathematically as 1 microvolt = (1 \times 10^{-6}) volts. This unit of measurement is important in various applications, particularly in electronics and telecommunications, where very small voltages are often encountered.

Understanding the prefixes in the metric system helps reinforce why this answer is correct. The prefix "micro-" denotes a factor of (10^{-6}), which directly correlates to one millionth. This makes it the correct and precise representation of one microvolt.

The other choices present various misinterpretations of voltage measurements. One million volts and one thousand kilovolts represent much higher voltage levels, which are not related to microvolts. Similarly, one one-thousandth of a volt translates to one millivolt, which is significantly larger than a microvolt. Overall, the only definition that aligns correctly with the established electrical measurements is the one that refers to one millionth of a volt.