The correct answer is option 3: Western Ghats. The western coasts of India receive very high rainfall in summer primarily because of the presence of the Western Ghats mountain range. The Western Ghats act as a barrier to the monsoon winds coming from the Arabian Sea. As the warm and moisture-laden winds from the Arabian Sea hit the Western Ghats, they are forced to rise, leading to the formation of clouds and heavy rainfall.

Option 1, tropical location, is not the main reason for the high rainfall on the western coasts of India. While India does have a tropical climate, the specific factor causing the high rainfall in summer is the presence of the Western Ghats.

Option 2, nearness to the sea, is partially correct as the western coasts of India do receive high rainfall due to their proximity to the Arabian Sea. However, the primary reason for the high rainfall is the Western Ghats.

Option 4, Himalayas, is incorrect. The Himalayas are located in northern India and do not directly influence the rainfall on the western coasts of India.

In conclusion, the Western Ghats are responsible for the high rainfall on the western coasts of India in summer.