Final answer:
The midpoint of the IQ scores for 7th-grade students is 100, which falls exactly between 85 and 115, the range representing one standard deviation above and below the mean IQ.
Step-by-step explanation:
The midpoint of the IQ scores for 7th-grade students is the value that is exactly in the middle of the range of average IQ scores. Since the average IQ according to most tests is 100 and standard deviation is 15 points, the middle 50 percent of IQs, representing the second and third quartiles, would be one standard deviation above and below the mean, which is between 85 and 115. Therefore, the midpoint would be halfway between these two values, which calculates to (85 + 115) / 2 = 100. So, the answer to the student's question is a. 100.