The correct answer is option 1, flint glass. Optical glass refers to the type of glass that is specifically designed for applications in optics, such as lenses and prisms. Flint glass is one type of optical glass that is commonly used in the construction of spectacles or eyeglasses.
Option 2, Crookes glass, is not the correct answer. Crookes glass is a type of glass that is specially designed to be resistant to heat and high temperatures, and it is mainly used in laboratories for scientific experiments and equipment.
Option 3, quartz glass, is also not the correct answer. Quartz glass is a type of glass that is composed mainly of silicon dioxide (SiO2) and is known for its excellent transparency to ultraviolet and infrared radiation. It is often used in optics for applications such as lenses, prisms, and windows.
Option 4, hard glass, is not the correct answer either. Hard glass is a general term used to describe glass that has been specially treated and processed to make it more resistant to breakage or scratching. It is not specifically designed for optical applications like spectacles.
In conclusion, the correct answer is option 1, flint glass, which is commonly used in the construction of spectacles and other optical devices