Which system of social stratification was in the final stages of breaking down when karl marx developed his ideas?

Serfdom

Explanation:

Karl Marx (1818-1883) is considered as the father of socialism. He started developing his ideas as a journalist and strongly criticised the Russian monarchy ruled by Russian emperors known as Tsars. In an absolute monarchy, nobility was the highest social class. Noblemen were educated and had privileges but most people in Imperial Russia were serfs, the lowest social class.  

In most serfdoms, serfs were legally part of the land, and if the land was sold, they were sold with it. In England, serfdom lasted up to the 1600s, in France until 1789. In most other European countries serfdom lasted until the early 19th century.

the answer your looking for is c. : )