Final answer:
The observation that best indicates adequate fluid replacement in a child on the burn unit is urinary output of 32 mL per hour.
Step-by-step explanation:
The observation that best indicates adequate fluid replacement in a child on the burn unit is urinary output of 32 mL per hour. This is because one of the important indicators of proper hydration is the adequate production of urine. A urinary output of 32 mL per hour indicates that the child's kidneys are functioning well and able to eliminate waste products and excess fluids from the body.
While moist oral mucus membranes and normal skin turgor are also important signs of hydration, they can be influenced by other factors and may not be as reliable as the urinary output measurement. Thirst is not a reliable indicator of hydration as it can be affected by various factors such as temperature and the child's subjective perception of thirst.