Solution:The Tamil Nadu coast does remain dry during the South- West monsoon season. This is because it is situated parallel to the Bay of Bengal branch of the South-West monsoon.The prevailing winds during the monsoon season blow from the South-West, bringing moisture-laden winds from the Bay of Bengal towards the Indian subcontinent. However, the Tamil Nadu coast lies in the rain shadow area of the Arabian Sea branch of the South-West monsoon.
The Western Ghats mountain range acts as a barrier, blocking the moisture-laden winds from the Arabian Sea, resulting in less rainfall along the Tamil Nadu coast.
Therefore, both the assertion (A) and the reason (R) are true, and (R) provides the correct explanation for (A).