Answer:
The type of error that the sociologist has made when he fails to reject the null hypothesis when it is false (and thus should have rejected it) is a:
c) Type II error.
Step-by-step explanation:
In Statistics, Type II error is made when the null hypothesis is accepted when it is not true (false). The sociologist should have rejected the null hypothesis, but he fails to reject it. He has, therefore, made a Type II error. It is also called a "false negative." On the other hand, a Type I error is committed when the sociologist rejects the null hypothesis when he should have accepted it. A Type I error is also called a "false positive."