Which of the following is a sign of acute renal failure?

Fluid retention is a key sign of acute renal failure. In this condition, the kidneys are unable to effectively filter waste and excess fluid from the blood, leading to a buildup of fluid in the body. This can manifest as swelling in various areas, particularly in the legs, ankles, and around the eyes. Additionally, fluid retention can contribute to an increase in blood pressure and may lead to more serious complications such as pulmonary edema, where fluid accumulates in the lungs.

The other options do not typically indicate acute renal failure. A persistent urge to urinate may be associated with urinary tract infections or other urinary conditions rather than kidney failure itself. Chest pain can be caused by a variety of issues, including cardiac conditions or muscle strain, but it is not a direct sign of renal failure. A gradual decline in kidney function is more indicative of chronic kidney disease rather than the sudden onset characteristic of acute renal failure. Thus, fluid retention correctly represents a symptom associated with the acute condition.