Turbidity in water can be measured using which of the following tools?

The correct choice, the Secchi disk, is specifically designed to measure water clarity, which is directly related to turbidity. Turbidity refers to the cloudiness or haziness of a fluid caused by large numbers of individual particles that are generally invisible to the naked eye. The Secchi disk is a flat, circular disk that is lowered into the water until it is no longer visible. The depth at which the disk disappears gives a measure of the water’s clarity, thus providing an indirect measurement of turbidity.

The other tools mentioned are not appropriate for measuring turbidity. A pH meter is used to measure the acidity or alkalinity of a solution, a thermometer measures temperature, and a hydrometer assesses the density or specific gravity of liquids. None of these tools provide insights into particulate matter or the clarity of water like the Secchi disk does.