Question

Which of the following is used for making optical instruments?
A. $Si{{O}_{2}}$
B. $Si$
C. $Si{{H}_{4}}$
D. None

Answer 1

Hint: Flint glasses, which is a material formed by the combination of a mixture of silicate of potassium and lead and has a chemical formula ${{K}_{2}}O.P{{b}_{2}}O.4Si{{O}_{2}}$ is generally used for processing and making several optical instruments, where silica plays as the important ingredient. Find the option having the formula of silica.

Complete step by step answer:
Optical instruments are the devices that process light waves to enhance the look of an image for a clear view. Besides magnifying the distant or tiny images, these devices are used to analyse the properties of optical materials and light.
So, these optical instruments are made of different types of glasses which are made by mixing certain compounds, melting them and letting the mass slowly solidify, so that an amorphous material is obtained.
Silica (i.e. amorphous silicon dioxide, with chemical formula $Si{{O}_{2}}$) is widely used in optics that is making of optical instruments, either as pure substance (i.e. fused silica, fused quartz) or more frequently as a mixture with other compounds (silicate glasses). Mixing of silica with additional compounds will further lead to related materials such as borosilicates, aluminosilicates, german silicates, etc.
Thus, looking each option the first option shows the same formula that to the chemical formula of silica ($Si{{O}_{2}}$) while other options states the formula of silicone and silane ($Si{{H}_{4}}$).
So, the correct answer is “Option A”.

Note: Possibly you may get confused with the fourth option that is silane with chemical formula $Si{{H}_{4}}$. But silane is generally used as coupling agents to adhere fibres such as glass fibres and carbon fibres to certain polymer matrices, in order to stabilise the composite material. In short, silane is used as a coating agent for the glass fibres while most of the optical instruments are based on silica and thus, they are sometimes referred to as silica fibres.