Constant mass is achieved when further drying at 230 ± 9 °F changes mass by no more than 0.1 percent.

• A. It is defined by temperature
• B. True
• C. It is 0.5%
• D. It depends on sample size

Answer: (B)

Constant mass is determined by stability of the weight during the drying process. You dry the sample at the specified temperature and keep weighing it until subsequent weighings no longer show a meaningful change. The rule used here is that the mass change between weighings must be 0.1 percent or less. That tiny, fixed percentage is what defines when the sample is considered dry enough to stop drying and declare the mass constant. The temperature setting (230 ± 9 °F) provides the drying environment, but the stopping criterion is the balance stability itself, not the temperature value. The 0.1 percent threshold is the standard limit, not 0.5 percent, and the decision is not governed by sample size in any way that would change the criterion—the percentage ensures consistency across different sample amounts.