Consider the following statements about the megacities of India: I. Population of each megacity is more than 5 million. II. All the megacities are important sea ports. III. Megacities are either national or State capitals. Which of these statements are correct?

Statement I is correct because in the Indian context, a megacity is typically defined as a metropolitan area with a population exceeding 5 million. Major Indian cities like Mumbai, Delhi, Kolkata, Chennai, Bengaluru, and Hyderabad all meet this threshold.

Statement II is incorrect because not all megacities are seaports. While Mumbai, Chennai, and Kolkata are coastal or near-coastal, cities like Delhi, Bengaluru, and Hyderabad are landlocked and located in the interior of the country.

Statement III is correct because all current Indian megacities serve as either the national capital or the capital of their respective states. For example, Delhi is the national capital, while others like Mumbai, Chennai, Kolkata, Bengaluru, and Hyderabad are state capitals.

Therefore, since statements I and III are correct and statement II is false, the correct option is D.