Detailed Explanation:

Answer: Option 1 — Sumatra

Sumatra is the geographically closest island to Great Nicobar, separated by the Great Channel (also known as the Six Degree Channel or Strait of Sumatra). The distance between the southernmost point of Great Nicobar and the northern tip of Sumatra (Aceh province, Indonesia) is approximately 145–150 km.

In contrast, Sri Lanka is located about 1,200 km to the west of the Nicobar Islands across the Bay of Bengal. Java is situated to the southeast of Sumatra, at a distance of over 1,500 km from Great Nicobar. Borneo is positioned much further east in the Malay Archipelago, making it the most distant among all options. Therefore, Sumatra is the correct answer.