Final answer:
The patient who gained 3.5 kg due to fluid overload has gained approximately 3.5 liters of fluid.
Step-by-step explanation:
The question asks to convert the patient's weight gain of 3.5 kg in 24 hours into the volume of fluid gained. To convert kg to liters, we can use the fact that 1 kg of water is approximately equivalent to 1 liter of water, because the density of water is roughly 1 kg/L. Therefore, if a patient gains 3.5 kg from fluid, this is equivalent to a fluid gain of 3.5 liters.