The correct answer is D. Platinum cobalt scale.
Turbidity is a measure of the cloudiness of a liquid. It is caused by the presence of suspended particles in the liquid. The higher the turbidity, the more particles are present and the cloudier the liquid will appear.
The platinum cobalt scale is a logarithmic scale that is used to measure turbidity. It is based on the amount of light that is scattered by the suspended particles in the liquid. The higher the turbidity, the more light will be scattered and the lower the reading on the platinum cobalt scale will be.
The standard silica scale and the standard cobalt scale are two other scales that are used to measure turbidity. However, these scales are not as accurate as the platinum cobalt scale.
The standard silica scale is based on the amount of silica that is required to produce a certain level of turbidity. The standard cobalt scale is based on the amount of cobalt that is required to produce a certain level of turbidity.
Both of these scales are less accurate than the platinum cobalt scale because they are not as sensitive to the amount of suspended particles in the liquid.