Which island nation is located southeast of India?

The island nation located southeast of India is Sri Lanka. This island is situated in the Indian Ocean, just off the southeastern tip of the Indian mainland. Geographically, it is separated from India by the Palk Strait and is known for its distinct cultural heritage, diverse ecosystems, and significant historical sites.

In relation to the other options, the Maldives is located southwest of India and consists of a chain of atolls and islands, making it quite different in location from Sri Lanka. Bali is part of Indonesia and is situated to the east of India, whereas Sumatra, also an Indonesian island, lies further southeast of the Indian subcontinent. Thus, while these other locations are notable in their own right, Sri Lanka is uniquely positioned directly southeast of India, making it the correct answer.