Which of the following is equal to 1 liter in the metric system?

In the metric system, a liter is a unit of volume that is defined as equivalent to 1000 milliliters. This relationship is part of the metric system's base-10 structure, where each unit is a multiple or fraction of others by powers of ten. Specifically, since there are 1000 milliliters in 1 liter, this means that when converting from liters to milliliters, you multiply by 1000.

To understand this in context, 100 milliliters is only a small fraction of a liter (1/10th of a liter), and 10 centiliters is also less than a liter, as it equals 100 milliliters since 1 centiliter equals 10 milliliters. The option stating 10000 milliliters greatly exceeds 1 liter, as it represents 10 liters (since 10000 divided by 1000 yields 10). Thus, 1000 milliliters is the correct answer, as this directly reflects the conversion within the metric system for liters.