Step 1: Understanding the Question:
The question asks which school of thought in human geography used the ideas of Karl Marx to explain social inequality.
Step 2: Key Fact or Approach:
In human geography, the Radical school (1970s) used Marxist ideas to explain poverty, deprivation and inequality as results of the capitalist system. Other schools had different focus areas.
Step 3: Check option (A).
The Positivist school stresses quantitative methods, laws and models. It does not use Marxist theory to explain inequality, so this option is wrong.
Step 4: Check option (B).
The Humanistic school focuses on human beings, their values, perception and experience of places. It is not built on Marxian theory, so this option is wrong.
Step 5: Check option (C).
The Radical school grew in the late 1960s and 1970s. It applied Marxian theory to explain poverty, social inequality and the unequal use of resources. This option is correct.
Step 6: Check option (D).
The Behavioural school studies how people perceive their environment and how perception affects decisions. It does not use Marxian theory, so this option is wrong.
Final Answer:
Marxian theory was applied by the Radical School of Thought. The correct option is (C), option number 3.