Explanation:

- The theory of “social engineering” was propounded by Roscoe Pound.

- Roscoe Pound (Option 2) was an American legal scholar who emphasized that law should be used as a tool for social engineering, i.e., balancing competing interests in society for the betterment of social order.

- Salmond (Option 1) was a British jurist known for his writings on jurisprudence, but not for the theory of social engineering.

- Hart (Option 3), known for his analytical approach to law, contributed concepts such as the rule of recognition but didn't propose social engineering.

- Option 4 (None of the above) is incorrect as Roscoe Pound is the right answer.