Step 1: Understanding the Question:
This question is about which thinker criticised capitalism by arguing that workers are not paid the full value of what they produce.
Step 2: Identify the correct thinker.
Karl Marx argued that under capitalism, workers create more value through their labour than they receive back as wages, and the capitalist class keeps this extra value, which he called surplus value. He saw this as a built in exploitation of labour inside the capitalist system.
Step 3: Why the other options are wrong.
Adam Smith is known for supporting free markets and explaining how they can create wealth, not for calling capitalism exploitative. Alfred Gell was an anthropologist who worked on art and agency, not on capitalist economic theory. Max Weber studied capitalism too, but through ideas like rationalisation and the Protestant work ethic, not through the specific idea of labour exploitation.
Final Answer:
Karl Marx considered the capitalist economy to be based on the exploitation of labour. This is option (B).