GENERAL KNOWLEDGE

Detailed explanation-1: -An atoll is a ring-shaped coral reef, island, or series of islets. An atoll surrounds a body of water called a lagoon. Sometimes, atolls and lagoons protect a central island. Channels between islets connect a lagoon to the open ocean or sea.

Detailed explanation-2: -An atoll is a roughly circular (annular) oceanic reef system surrounding a large (and often deep) central lagoon. Examples of this reef type are common in French Polynesia, the Caroline and Marshall Islands, Micronesia, and the Cook Islands.

Detailed explanation-3: -Coral reefs begin to form when free-swimming coral larvae attach to submerged rocks or other hard surfaces along the edges of islands or continents. As the corals grow and expand, reefs take on one of three major characteristic structures-fringing, barrier or atoll.