Final answer:
The population variance is calculated by squaring the standard deviation. Given the standard deviation is 3, the population variance is 9.
Step-by-step explanation:
The question deals with the concept of population variance in statistics, which is a measure of how much individual scores in a population deviate from the population mean. To find the population variance, we need to square the standard deviation. Given that the population standard deviation (σ) is 3, the population variance is calculated as σ^2, which is 3^2 = 9.
Therefore, the correct answer to the question 'A population of N = 10 scores has µ = 21 and σ = 3. What is the population variance?' is d. 9.