The correct answer is D. The Kula (Family).
The Kula was the basic unit of social and political organization in the Rig Vedic period. It was a patrilineal extended family, consisting of a man, his wife or wives, their children, and unmarried siblings. The Kula was headed by the eldest male, who was responsible for making decisions on behalf of the family.
The Kula was a self-sufficient unit, with its own land, livestock, and other resources. It was also a religious unit, with its own rituals and ceremonies. The Kula was the basic unit of society in the Rig Vedic period, and it played a vital role in the social, political, and religious life of the people.
The other options are incorrect.
A. The Samaj is a modern term used to refer to a society or community. It is not a term that was used in the Rig Vedic period.
B. The Smriti is a collection of Hindu laws and scriptures. It is not a term that was used to refer to a social or political organization in the Rig Vedic period.
C. The Sabha is a council of elders. It is not a term that was used to refer to a social or political organization in the Rig Vedic period.