Final answer:
Docusate sodium is the surfactant laxative and it works by softening the stool and reducing its surface tension to help alleviate constipation.
Step-by-step explanation:
The surfactant laxative is Docusate sodium (B) which is commonly used to relieve constipation. It works by softening the stool and allowing water to penetrate it, making it easier to pass. Docusate sodium functions by reducing the surface tension of the stool, which helps to increase the mixing of liquids within the intestines.