The correct answer for this question is option 3: Their leeward location. The eastern slopes of the Western Ghats experience low rainfall due to their leeward location.

To understand this, let`s first understand the concept of leeward. The leeward side of a mountain refers to the side that is sheltered or protected from prevailing winds. In this case, the Western Ghats act as a barrier and block the moisture-laden winds coming from the Arabian Sea. As a result, the western slopes of the Western Ghats receive heavy rainfall, while the eastern slopes, being on the leeward side, experience low rainfall.

Option 1, the straight West Coast, is not the primary reason for low rainfall on the eastern slopes. Option 2, the lack of winter depressions, may contribute to low rainfall, but it is not the main reason. Option 4, the heights of the Chats, may affect the distribution of rainfall, but it does not solely explain the low rainfall on the eastern slopes.

In conclusion, the leeward location of the eastern slopes of the Western Ghats is the primary reason for their low rainfall.