Explanation:

- Option 1: R. Firth – While Raymond Firth was a prominent social anthropologist, he did not coin the term "social organisation."

- Option 2: Radcliffe-Brown – Radcliffe-Brown is widely known for coining and popularising the concept of "social organisation." He focused on the structure and function of society.

- Option 3: Gerth and Mills – They are known for their work on social theory but not specifically for coining "social organisation."

- Option 4: Ginsberg – Ginsberg contributed to sociology but is not credited with this concept.

Correct answer:

Option 2: Radcliffe-Brown