Explanation:

- Option 1: Talcott Parsons

- A functionalist sociologist known for his work on the nuclear family.

- Argued that the nuclear family serves crucial functions in modern societies, like socialization and stabilization.

- However, he didn't specifically consider it a universal grouping.

- Option 2: Ogburn and Nimcoff

- Sociologists who studied family structures and their functions.

- Their focus was on the evolving roles and functions of family in society.

- They did not define the nuclear family as a universal grouping.

- Option 3: G.P. Murdock

- A well-known anthropologist who studied family structures worldwide.

- Defined the nuclear family as a universal social grouping found in all societies.

- Option 4: Ann Oakley

- A feminist sociologist who studied family roles and gender dynamics.

- Critiqued traditional family structures, focusing on gender inequalities rather than universality.