The correct answer is option 'D' - October to November.

Tamil Nadu is located on the southeastern coast of India and experiences a tropical wet and dry climate. The region receives most of its rainfall during the northeast monsoon season, which generally occurs from October to December. Let's explore why October and November are the months when Tamil Nadu coast receives the most rainfall.

1. Northeast Monsoon:
The northeast monsoon, also known as the winter monsoon or the retreating monsoon, is a reversal of winds that brings rainfall to Tamil Nadu. During this season, the northeast trade winds blow from the land towards the sea, carrying moisture from the Bay of Bengal. As a result, the eastern coast of Tamil Nadu receives heavy rainfall.

2. Reason for Heavy Rainfall:
The northeast monsoon is primarily influenced by the retreating southwest monsoon, which brings abundant rainfall to the western coast of India from June to September. As the southwest monsoon weakens and withdraws, it sets the stage for the onset of the northeast monsoon. The moisture-laden winds from the Bay of Bengal collide with the dry winds from the land, leading to the formation of rain-bearing clouds and subsequent rainfall along the Tamil Nadu coast.

3. Rainfall Distribution:
During the months of October and November, Tamil Nadu receives the highest amount of rainfall due to the northeast monsoon. Coastal areas such as Chennai, Cuddalore, and Nagapattinam experience heavy rainfall during this period. The rainfall gradually decreases in December as the northeast monsoon weakens.

4. Importance of Northeast Monsoon:
The northeast monsoon is crucial for Tamil Nadu's agriculture as it provides much-needed water for irrigation. The rainfall during this season replenishes groundwater levels and contributes to the growth of crops such as paddy, pulses, and millets.

In conclusion, the Tamil Nadu coast receives most of its rainfall during the months of October and November due to the influence of the northeast monsoon. This rainfall is essential for the region's agriculture and overall water availability.

Tamilnadu lies on the leeward side for the south west monsoon starts retreating after mid- September, North East monsoon sets in during mid-october. Tamilnadu lies on the windward side for these winds and hence gets more rainfall during the winter season. Therefore, there is getting most of the rainfall in the months from October to November.