Where are atolls?
Small clusters of islands, generally they have little elevation above sea-level.
An island is land completely surrounded by water what geography term is used to describe the opposite of this condition?
There are lakes, which are bodies of water completely surrounded by land (landlocked). Or, there are atolls. Atolls are islands of corals which surround a lagoon, some partially or some completely. Atolls are surrounded by water as well, which means they are just a circle of land surrounding and surrounded by water.
Bryan (1953) lists about 400 atolls. The full article is available through http://www.botany.hawaii.edu/faculty/duffy/arb/019-23/v019-23.pdf. This is not a definitive list as the definition of an atoll is still the subject of discussion discussion. Bryan, E.H., 1953. Check list of atolls. Atoll Res. Bull., 19: 1-38.
The U.S. used the pacific atolls because they were isolated from large population centers and because the Marshal Islands (where many of these atolls were) were entirely under U.S. control after WW2, so could freely involuntarily evacuate indigenous populations of the atolls that testing was planned on. The USSR did all of their testing inland for security reasons (they also did not have control over any atolls). The British did much of their testing inland…