Information:  - Aragonite is a carbonate mineral, one of the two most common, naturally occurring, crystal forms of calcium carbonate, CaCO (the other form being the mineral calcite). It is formed by biological and physical processes, including precipitation from marine and freshwater environments.  - Limestone is a sedimentary rock, composed mainly of skeletal fragments of marine organisms such as coral, forams and molluscs. Its major materials are the minerals calcite and aragonite, which are different crystal forms of calcium carbonate (CaCO).  - Corals are marine invertebrates in the class Anthozoa of phylum Cnidaria. They typically live in compact colonies of many identical individual polyps. The group includes the important reef builders that inhabit tropical oceans and secrete calcium carbonate to form a hard skeleton.  - Hobart is the capital and most populous city of the Australian island state of Tasmania. It is the least populated state capital in Australia. Founded in 1803 as a penal colony, Hobart is Australia's second oldest capital city after Sydney, New South Wales. The city is located in the state's south-east on the estuary of the Derwent River, making it the most southern of Australia's capital cities. Its harbour forms the second-deepest natural port in the world.  - Australia, officially the Commonwealth of Australia, is a country comprising the mainland of the Australian continent, the island of Tasmania and numerous smaller islands. It is the world's sixth-largest country by total area. The neighbouring countries are Papua New Guinea, Indonesia and East Timor to the north; the Solomon Islands and Vanuatu to the north-east; and New Zealand to the south-east. Australia's capital is Canberra, and its largest urban area is Sydney.  - Calcium carbonate is a chemical compound with the formula CaCO. It is a common substance found in rocks as the minerals calcite and aragonite (most notably as limestone, which contains both of those minerals) and is the main component of pearls and the shells of marine organisms, snails, and eggs. Calcium carbonate is the active ingredient in agricultural lime and is created when calcium ions in hard water react with carbonate ions to create limescale. It is medicinally used as a calcium supplement or as an antacid, but excessive consumption can be hazardous.  - Tasmania (abbreviated as Tas and known colloquially as "Tassie") is an island state of the Commonwealth of Australia. It is located to the south of the Australian mainland, separated by Bass Strait. The state encompasses the main island of Tasmania, the 26th-largest island in the world, and the surrounding 334 islands. The state has a population of around 518,500, just over forty percent of which resides in the Greater Hobart precinct, which forms the metropolitan area of the state capital and largest city, Hobart.  - Montgomery Rocks comprises a pair of rocky dolerite and limestone islets , with a combined area of 3.69 ha and a high point of 50 m , part of the Hibbs Pyramid Group , lying close to the central western coast of Tasmania .  - Bass Strait is a sea strait separating Tasmania from the Australian mainland, specifically the state of Victoria.  - Sedimentary rocks are types of rock that are formed by the deposition and subsequent cementation of that material at the Earth's surface and within bodies of water. Sedimentation is the collective name for processes that cause mineral and/or organic particles (detritus) to settle in place. The particles that form a sedimentary rock by accumulating are called sediment. Before being deposited, the sediment was formed by weathering and erosion from the source area, and then transported to the place of deposition by water, wind, ice, mass movement or glaciers, which are called agents of denudation. Sedimentation may also occur as minerals precipitate from water solution or shells of aquatic creatures settle out of suspension.  - Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate (CaCO). The Mohs scale of mineral hardness, based on scratch hardness comparison, defines value 3 as "calcite".    After reading the paragraphs above, we are interested in knowing the entity with which 'montgomery rocks' exhibits the relationship of 'instance of'. Find the answer from the choices below.  Choices: - area  - capital  - cause  - chemical compound  - city  - class  - collective  - colony  - continent  - country  - crystal  - formula  - ingredient  - island  - limestone  - material  - mineral  - population  - precinct  - precipitation  - river  - rock  - scale  - sea  - stable  - state  - strait  - supplement  - the city  - two  - water  - wind
The answer to this question is:
island