Step 1: Analyze the options.
- Option (a): The gold mine region of the Australian desert is known to have mineral deposits that lead to population density.
- Option (b): The mineral oil region of South West Asia is rich in oil deposits and is also densely populated due to the extraction and trade of oil.
- Option (c): The Chhota Nagpur region in India is rich in minerals such as coal, iron ore, and mica, which contribute to its population density.
- Option (d): The prairie grassland region in North America is primarily an agricultural region, and although it has some resources, it is not typically dense in mineral deposits.
Step 2: Conclude the incorrect factor.
- The prairie grassland region in North America is not a mineral-producing region, hence it is the incorrect factor in the list.
Final Answer:
The incorrect factor is (d) Prairie grassland region in North America.