Which one of the following statements about glass is not correct?
Glass is often said to be a supercooled liquid.
Glass has no definite melting point.
Soda glass is harder than pyrex glass.
Boron is present in pyrex glass.
Answer is Wrong!
Answer is Right!
This question was previously asked in
UPSC NDA-2 – 2019
B) Due to its amorphous nature, glass does not have a specific melting point. It softens gradually over a range of temperatures. This statement is correct.
C) Soda-lime glass (soda glass) is the most common type of glass (window panes, bottles). Pyrex is a brand of borosilicate glass, which contains boron oxide (B₂O₃) in addition to silica. The addition of boron oxide significantly changes the properties, making it more resistant to thermal shock and chemical corrosion, and generally harder and more resistant to scratches compared to soda-lime glass. Therefore, soda glass is *not* harder than pyrex glass; it is softer.
D) Pyrex glass is a type of borosilicate glass, meaning it contains boron (specifically in the form of boron oxide). This statement is correct.