Final answer:
The concentration of glucose in the unknown sample is lower than the standard because its absorbance reading of 0.20 is lower than the standard's absorbance reading of 0.30.
Step-by-step explanation:
The value of the unknown in a glucose determination that was read on a spectrophotometer can be interpreted by comparing the absorbance readings of the unknown and the standard. In this case, the absorbance reading of the standard is 0.30, while the absorbance reading of the unknown is 0.20. Absorbance is directly proportional to the concentration of the substance being measured, assuming a linear relationship and uniform path length and other conditions.
Therefore, since the absorbance of the unknown (0.20) is lower than the absorbance of the standard (0.30), the concentration of glucose in the unknown sample is lower than the standard. This means the correct answer to the question is: A) Lower than the standard.