The correct answer is: b) Decentralized chiefdoms.
Mizo society was historically organized into decentralized chiefdoms. This means that there was no single ruler or government, but rather a number of different chiefs who ruled over their own territories. The chiefs were elected by the people and were responsible for settling disputes, leading the people in war, and organizing religious ceremonies.
Option a) is incorrect because Mizo society was not organized into large centralized kingdoms. There were a number of different chiefdoms, but they were not united under a single ruler.
Option c) is incorrect because Mizo society was not organized into egalitarian communes. The chiefs had more power than the ordinary people, and they were not elected by the people.
Option d) is incorrect because British-style administrative districts were not established in Mizoram until the 19th century.