Marx argued that throughout history, society has transformed from feudal society into Capitalist society, which is based on two social classes, the ruling class (bourgeoisie) who own the means of production (factories, for example) and the working class (proletariat) who are exploited (taken advantage of) for their ...

Which group exploits the working class by taking more of the value of the work of the laborers than they repay in wages?

The Bourgeoisie group exploits the working class by taking more of the value of the work of laborers than they repay in wages.

What group sells its labor to the bourgeoisie in order to receive wages?

In capitalist societies, the bourgeoisie class owns the means of production while the proletariat class sells their labor to the bourgeoisie.