ANS:C - potentiometer

The pH value of sewage is typically determined using a potentiometer, which is a device commonly employed in laboratory settings for pH measurement. A potentiometer, also known as a pH meter, utilizes a glass electrode and a reference electrode to measure the electrical potential difference between them, which is then converted into a pH value. Imhoff cones are not used for pH measurement but rather for settling and measuring the sedimentation of solids in wastewater samples. Turbidimeters, on the other hand, are instruments used to measure the turbidity or cloudiness of water caused by suspended particles, which is different from measuring pH. Therefore, the correct answer is potentiometer when determining the pH value of sewage.