There are many islands that lies between Sulawesi and Sumatra, but the biggest one is Kalimantan or sometimes called as Borneo.
The island that lies between Java and Lombok is Bali.
Some of the largest islands in Indonesia are Sumatra, Java, and Celebes. Sumatra is the largest of all the islands in Indonesia with an area of 164,000 square miles. Indonesia is made up of over 18,000 islands.
Sumatra
a small volcanic island in Indonesia between Java and Sumatra; its violent eruption in 1883 was the greatest in recorded history
That would be the Strait of Malacca.
That point is one of an infinite number of points on the Indonesian island of Sumatra. All of the others have different coordinates.
The island of Sumatra, which is part of Indonesia, is located at 0 latitude and 100 east longitude. Specifically, Kinali, West Pasaman in West Sumatra is located at these coordinates.
Mount Krakatoa is located in Indonesia, between the islands of Java and Sumatra. It is part of the Krakatoa volcanic group, which includes several other volcanic cones. The most famous eruption of Krakatoa occurred in 1883, causing massive destruction and tsunamis in the region.
Krakatoa lies in the Sunda Strait, between Java and Sumatra in the Indonesian province of Lampung. It is near the Indonesian island of Rakata.
The Indian Ocean. The volcanic island of Krakatoa lies between the Indonesian islands of Java, and Sumatra.
Java lies between Sumatra to the west and Bali to the east. Borneo lies to the north and Christmas Island is to the south. Java is surrounded by the Java Sea to the north, Sunda Strait to the west, the Indian Ocean to the south and Bali Strait and Madura Strait in the east.