Which of the statements about glass are correct ? 1. Glass is a super-cooled liquid having infinite viscosity 2. Violet coloured glass is obtained by adding Mn02 3. Glass is a man made silicate 4. Glass is a crystalline substance Select the correct answer using the code given below :

Glass is scientifically defined as a super-cooled liquid because it is an amorphous solid that lacks a long-range crystalline structure [t4][t5]. While it appears solid, it possesses extremely high (effectively infinite) viscosity at room temperature, preventing observable flow [t3][t7]. Statement 2 is correct as manganese dioxide (MnO2) is a common additive used to impart violet or purple hues to glass by controlling the oxidation state of manganese (Mn3+) [t1][t2][t6]. Statement 3 is accurate because most commercial glass is a man-made silicate, primarily composed of silica (SiO2) derived from sand, often mixed with sodium and calcium oxides [c2][t4][t8]. Statement 4 is incorrect because glass is an amorphous (non-crystalline) substance, unlike quartz which has a hexagonal crystalline structure [c2][t5][t8]. Therefore, statements 1, 2, and 3 are correct.

Sources

1. [1] https://en.m.wikipedia.org/wiki/Glass
2. [2] http://www.hbni.ac.in/phdthesis/phys/PHYS01200704024.pdf
3. [3] https://www.sciencedirect.com/science/article/pii/S259015911930024X
4. [4] https://www.nature.com/articles/s40494-016-0094-1
5. [5] https://www.sciencedirect.com/science/article/abs/pii/S2352409X18308174
6. [6] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 13: Types of Rocks & Rock Cycle > 13.5. Some Rock-Forming Minerals > p. 175