The incorrect statement is (a)  because  India's climate has characteristics of tropical as well as subtropical climate due to the tropic of cancer which passes through the middle of the country from the Rann of Kuchchh in the west to Mizoram in the east. Almost half of the country, lying south of the Tropic of Cancer belongs to the Tropical area.

C is also incorrect as in the question Eastern Ghats is mentioned rather than Western Ghats.

Introduction:
India is a diverse country with a varied climate. The climate of India is influenced by various factors, including its geographical location, the presence of the Himalayas, the monsoon winds, and the differential heating of land and sea. In this context, let us analyze the given statements regarding the factors determining the climate of India.

Incorrect Statement:
The incorrect statement regarding the factors determining the climate of India is:

Statement a: The subtropical region of India being far from the equator, experiences extreme climate.

Explanation:
The subtropical region of India, which includes areas like Rajasthan and parts of Gujarat, is located closer to the Tropic of Cancer and not far from the equator. Hence, the statement is incorrect.

Correct Statements:
Let us now examine the remaining statements:

Statement b: Differential heating of land and sea creates different air pressure zones that cause a reversal in the direction of monsoon winds.

Explanation:
- The differential heating of land and sea plays a crucial role in the formation of monsoons in India.
- During summer, the landmass of India heats up faster than the surrounding oceans, creating a low-pressure area over the land and a high-pressure area over the oceans.
- This contrast in air pressure leads to the onset of the southwest monsoon winds, which blow from the high-pressure area over the oceans towards the low-pressure area over the land.
- In winter, the reverse happens, as the land cools down faster than the oceans, creating a high-pressure area over the land and a low-pressure area over the oceans.
- This reversal in pressure causes the onset of the northeast monsoon winds, which blow from the high-pressure area over the land towards the low-pressure area over the oceans.
- Therefore, statement b is correct.

Statement c: The southern plateau remains dry due to its windward situation along the Eastern Ghats.

Explanation:
- The southern plateau of India, which includes regions like Deccan Plateau and Tamil Nadu, is located to the leeward side of the Western Ghats and not the Eastern Ghats.
- The Western Ghats act as a barrier and obstruct the southwest monsoon winds, causing them to rise and cool down, leading to heavy rainfall on the windward side.
- As a result, the leeward side, which includes the southern plateau, experiences a rain shadow effect and remains relatively dry.
- Therefore, statement c is incorrect.

Conclusion:
To summarize, the incorrect statement regarding the factors determining the climate of India is statement a, while statements b and c are correct. The differential heating of land and sea leads to the reversal of monsoon winds, and the southern plateau remains dry due to the rain shadow effect caused by the Western Ghats.