Explanation:
The turbidity of water refers to the cloudiness or haziness of water caused by suspended particles. It is an important parameter in water quality analysis as it can affect the transparency and aesthetic appearance of water. Turbidity is typically measured using a turbidimeter, and the unit of measurement varies depending on the method used.

Silicon dioxide, also known as silica, is a common mineral that can be found in various forms, including sand, quartz, and glass. It is often used as a standard to measure turbidity because it has consistent properties and is readily available. The standard turbidity produced by one milligram (mg) of silica in one litre of distilled water is called a Jackson Turbidity Unit (JTU).

Reasons for the Correct Answer:
The correct answer is option A, one Jackson Turbidity Unit (JTU). This is because the Jackson Turbidity Unit is a widely accepted unit of measurement for turbidity, particularly in the United States. It is based on the standard turbidity produced by one mg of silica in one litre of distilled water.

Other units of turbidity measurement include the Formazin Turbidity Unit (FTU) and the Nephelometric Turbidity Unit (NTU). The FTU is based on a standard prepared using formazin, a synthetic polymer. The NTU is based on the nephelometric method, which measures the scattered light at a 90-degree angle.

However, the JTU is specifically based on the turbidity produced by silica, making it the correct answer in this context. It is important to note that turbidity measurements can vary depending on the method and instrument used. Therefore, it is crucial to use standardized methods and units to ensure consistent and comparable results.

Conclusion:
In summary, the standard turbidity produced by one mg of silicon dioxide (silica) in one litre of distilled water is called a Jackson Turbidity Unit (JTU). This unit of measurement is widely accepted and used in the United States. Other units, such as the Formazin Turbidity Unit (FTU) and Nephelometric Turbidity Unit (NTU), are also used but are based on different standards and methods. It is important to use standardized methods and units to ensure consistent and comparable turbidity measurements.