Final answer:
The degree(s) of freedom that should be used for a chi-square test to test the hypothesis that a set of data represents a F2 ratio of 9:3:3:1 is 3.
Step-by-step explanation:
To test the hypothesis that a set of data represents a F2 ratio of 9:3:3:1, a chi-square test can be conducted. The degree(s) of freedom that should be used for this test is determined by the number of categories or groups being compared minus 1. In this case, there are 4 categories (9, 3, 3, and 1), so the degrees of freedom would be 4 - 1 = 3. Therefore, the correct answer is c) 3.