Final answer:
The statement that glass is an extremely viscous liquid is false; glass is an amorphous solid, characterized by its lack of a regular crystal structure and considered solid for practical and observable purposes.
Step-by-step explanation:
Glass is an amorphous solid, which means that it lacks a regular repeating crystal structure and does not crystallize as it cools. This can give glass properties that seem liquid-like over very long timescales, but for practical and observable purposes, glass is considered a solid. This misconception that glass is an extremely viscous liquid probably stems from observations of old windowpanes that are thicker at the bottom, suggesting flow over centuries. However, this phenomenon is due to glass manufacturing processes of the past, not because glass is a liquid. When glass is heated, it softens gradually rather than melting at a distinct point, which is characteristic of amorphous solids like rubber, plastic, and gels.
It's often said that glass, such as silica, forms when a liquid like molten quartz is cooled too quickly to arrange into a crystalline structure, resulting in a material with a random arrangement of SiO4 tetrahedra. This property is extremely useful in various applications due to its transparency and low coefficient of expansion, like in UV radiation lamps and cookware such as CorningWare that contains amorphous silica. Therefore, the statement that glass is an extremely viscous liquid is False.