Explanation:

- Volksgeist: Introduced by Friedrich Carl von Savigny in the early 19th century. It emphasizes the spirit of the people and cultural context in law's development.

- Imperative Theory of Law: This theory was advocated by philosophers like John Austin in the 19th century. It focuses on law as commands from a sovereign enforced by sanctions.

- Social Engineering: Coined by Roscoe Pound in the early 20th century. It sees law as a tool to engineer society effectively and balance competing interests.

- Social Solidarity: Associated with Émile Durkheim, also in the late 19th and early 20th centuries. It emphasizes the importance of law in maintaining social cohesion and harmony.

- Option 1: I, II, III, and IV does not fit the timeline as imperative law came before volksgeist.

- Option 2: II, I, IV, and III is correct as it follows the historical development.

- Option 3: III, IV, I, and II is incorrect as it mixes the early 20th-century ideas with earlier concepts.

- Option 4: II, I, III, and IV does not fit as social engineering was last.