Which unit of time is equivalent to 400 years?

The correct answer is Baktun. In the context of Mesoamerican calendar systems, particularly the Mayan calendar, a Baktun is defined as a period of 400 years. This value is particularly significant in the Long Count calendar, which the Maya used to track longer periods of time.

The other terms, though also part of Mesoamerican timekeeping, represent different lengths of time. A Katun is equivalent to 20 years, a Tun refers to a period of 360 days, and a Kin denotes a single day. Therefore, understanding these specific time units is crucial when interpreting the Mayan calendar and its historical significance.