Explanation:

- Understanding Soap Formation:

- Sodium salts in soap are typically created through a process called saponification.

- This involves reacting fats or oils with a strong alkali to yield soap and glycerol.

- Chemical Analysis:

- Option 1 - Sulphuric acid: An acid, not used in the basic saponification process.

- Option 2 - Sodium hydroxide: Correct, this strong alkali (also known as lye or caustic soda) reacts with fats and oils to form soap containing sodium salts.

- Option 3 - Nitric acid: An acid that does not participate in soap formation.

- Option 4 - Carbonic acid: Another weak acid, irrelevant for saponification.

- The correct answer is Sodium hydroxide from Option 2.