Option 1 states that glass is a super-cooled liquid with infinite viscosity. This statement is incorrect. Although there is a common misconception that glass is a super-cooled liquid, it is actually an amorphous solid.

Option 2 states that violet-colored glass is obtained by adding Mn02. This statement is correct. Manganese dioxide (MnO2) is commonly used as a colorant in glass manufacturing processes to achieve violet or purple hues.

Option 3 states that glass is a man-made silicate. This statement is correct. Glass is primarily made from silica, which is a natural compound found in abundance in the Earth`s crust. Silicate compounds are formed by combining silica with various other elements.

Option 4 states that glass is a crystalline substance. This statement is incorrect. Unlike crystalline substances, glass does not have a regular, repeating atomic structure. Instead, it has a disordered, amorphous structure.

In summary, the correct statements about glass are 2, 3, and 4.