MCQ Detailed View

Water is a unique substance with many unusual properties, one of which is its ability to exist in multiple crystalline phases. While most people are familiar with ordinary ice (ice Ih_hh), scientists have discovered 18 different crystalline phases of water, also called ice polymorphs. These phases form under varying pressure and temperature conditions, showing how versatile water molecules are in arranging themselves in solid structures.

The ordinary ice we see in everyday life is known as ice Ih_hh, which has a hexagonal crystal structure. Other phases, like ice II, ice III, ice IV, up to ice XVIII, are formed in laboratories using high pressures or very low temperatures. Each phase has a distinct molecular arrangement, density, and physical properties. For example, some ice polymorphs are denser than liquid water, while others are less dense.

The study of ice polymorphs is important in physical chemistry, crystallography, and planetary science. These phases help scientists understand water’s behavior in extreme conditions, such as in the deep oceans, glaciers, or on other planets and moons. High-pressure ice phases are thought to exist in the interior of planets like Neptune and Uranus, or in icy moons such as Europa and Ganymede.

Understanding the 18 crystalline phases of water highlights the versatility of hydrogen bonding. The ability of water molecules to form various hydrogen-bonded networks is what leads to the different crystal structures. Each phase is stable only within certain temperature-pressure ranges, making water an exceptional substance for scientific research.

Therefore, the correct answer is 18, representing all currently known crystalline phases of water, emphasizing its unique chemical and physical properties in solid form.