A researcher is interested in whether there are significant differences between men and women and religious preferences. In planning his hypothesis tests, the researcher identified gender as the independent variable and religious preferences (e.g., Catholic, Protestant, Jewish) as his dependent variable. Can the researcher use an independent-samples t test to test his hypothesis

An independent samples t test is one where the means of two independent groups are compared in order to find out if there is statistical evidence that shows if there is any significant difference in the associated population means of the samples being researched.

Now, in this question, one group sample which is "gender" is independent while the other one which is "religious preferences" is dependent. Since they are both not independent, it does not fit into the definition of the independent-samples t test defined above where both have to be independent.

Thus, this method can't be used for the research in the question.