Step 1: Recall the idea of surplus value.
The key clue is 'exploitation of labour', which is closely tied to the idea that a capitalist pays workers less than the value they actually produce.
Step 2: Match the idea to its author.
This surplus value theory belongs to Karl Marx, who built his entire critique of capitalism around this gap between what labour produces and what labour is paid.
Step 3: Separate Marx from the other thinkers.
Adam Smith praised market efficiency, Weber studied rationalisation and religion's role in capitalism, and Gell worked outside economic theory altogether, so none of them fit this specific exploitation based view.
Final Answer:
Option (B), Karl Marx, is correct.