Final answer:
The assay results are precise because the measurements are close to each other. The accuracy cannot be determined without the true value.
Step-by-step explanation:
The student asked whether the assay results (42.6 ppm, 43.5 ppm, 41.9 ppm, and 42.3 ppm) are accurate, precise, both, or neither. Accuracy refers to how close a measurement is to the true or accepted value, whereas precision refers to how close repeated measurements are to each other.
Without knowing the true or accepted value, we cannot assess accuracy. However, we can evaluate precision. Given that all four measurements are close to each other, differing by at most 1.6 ppm, we can conclude that the results are precise. Without additional information, we cannot conclude about accuracy.