Which of the following chemical compounds are known as Quartz crystals, normally used in quartz clocks etc.?

Answer: Option 3

Explanation:

Quartz is silicon dioxide, SiO2. Quartz is abundant in the Earth's crust, being the chemically simplest form of the silicates. It appears in many forms. A quartz crystal is a thin plate or small rod of quartz cut along certain lines and ground so that it can produce an electric signal at a constant frequency; used in crystal oscillators. Some materials, such as certain ceramics and quartz crystals, can produce electricity when placed under mechanical stress. The ability to convert voltage to and from mechanical stress is called piezoelectricity. Quartz crystals maintain a precise frequency standard, which helps to regulate the movement of a watch or clock, thus making the timepieces very accurate.