The correct answer is D) The ring dam size is too large. In the illustrated device, if oil is being discharged from port "N", it likely indicates that the ring dam size is too large. This would allow the oil to overflow the ring dam and be discharged, which is not the normal operation. The purpose of the ring dam is to contain the oil and prevent it from being discharged overboard. If the ring dam is too large, it cannot effectively contain the oil, leading to the observed oil discharge. The other options are incorrect because A) normal operation would not involve oil discharge, B) the device is not functioning as a clarifier, and C) a ring dam that is too small would more likely lead to oil spilling over the sides, not through port "N".