Which one among the following statements is not true for glass ?

[amp_mcq option1=”Sodium silicate is known as water glass.” option2=”Glass is also called super cooled liquid.” option3=”Crystallinity develops on cooling of the molten mass of the glass.” option4=”Coloured glasses can be made by adding different colouring materials.” correct=”option3″]

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UPSC CDS-2 – 2024

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Statement C, “Crystallinity develops on cooling of the molten mass of the glass,” is not true for glass.

Glass is defined as an amorphous solid. The process of glass formation (vitrification) involves cooling a molten material rapidly enough to prevent the atoms or molecules from arranging themselves into a regular, repeating crystalline structure. If crystallization occurs during cooling, the material becomes a crystalline solid, not glass.

Statement A is true: Sodium silicate solution (Na₂SiO₃) is widely known as water glass or liquid glass. Statement B is true: Glass is often described as a supercooled liquid because it lacks a long-range crystalline order, its structure resembles that of a liquid, although its viscosity is extremely high, giving it the mechanical properties of a solid. Statement D is true: Coloured glasses are made by adding small amounts of various metal oxides or other colouring agents to the glass composition before melting, which absorb or scatter specific wavelengths of light.

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