Final answer:
The gemstone with the greatest mass is the one that weighs 0.890 grams.
Step-by-step explanation:
The student asked which of the three gemstones has the greatest mass, with weights provided as 0.809 grams, 0.098 grams, and 0.890 grams. To find the greatest mass, we compare these numbers directly. The highest numerical value represents the greatest mass. In this case, 0.890 grams is the largest number, so it represents the highest mass among the three gemstones.