The correct answer is: D. 50 to 400 mm of rainfall a year.
The southern Deccan area is in a rain shadow and receives only 50 to 400 mm of rainfall a year. This is because the Western Ghats, a mountain range that runs along the western coast of India, blocks the moisture-laden winds from the Arabian Sea. As a result, the southern Deccan area is much drier than the northern part of India.
The options A, B, and C are incorrect because they do not represent the range of rainfall that the southern Deccan area receives. Option A is too high, option B is too low, and option C is not within the range of rainfall that the southern Deccan area receives.