Final answer:
The density of water at 40.0°C would be slightly less than its maximum at 4°C, and when the water is heated to 70.0°C, the density decreases due to thermal expansion.
Step-by-step explanation:
The question pertains to the density of water at different temperatures. At 40.0°C, the density of water is not provided in the reference materials, but it is known that the density of water is highest at 4°C and decreases both when the temperature increases above this point and when it falls below this point. Therefore, without exact figures from a reference like the Chempendix, it is reasonable to infer that the density of water at 40.0°C would be slightly less than the maximum density it has at 4°C, which is approximately 1.0 g/mL. When the temperature of the water sample is increased to 70.0°C, thermal expansion will cause it to become less dense.
Thus, the density decreases when the temperature of the water sample is raised from 40.0°C to 70.0°C. The correct answer to the question, 'What happens to the density when the water sample is heated to a temperature of 70.0°C?' is option B: The density decreases.