Final answer:
Kant would expect you to tell the truth in this situation, as honesty is a moral duty and lying contradicts the categorical imperative.
Step-by-step explanation:
Kant, a well-known philosopher, emphasizes the importance of moral duty and universal principles. According to Kant's ethical theory, known as deontology, one should always act in accordance with moral rules called categorical imperatives. In this situation, if your roommate's murderous ex asks you where she is, Kant would expect you to tell the truth because honesty is a moral duty and lying is considered a contradiction of the categorical imperative. Kant believes that moral principles should be followed regardless of the consequences. Therefore, even though the situation may be difficult and potentially dangerous, telling the truth is what Kant would expect you to do.