Which word can be used to describe a well-reasoned argument?

The word "justifiable" is appropriate for describing a well-reasoned argument because it implies that the basis of the argument is sound, logical, and can be defended with evidence and reasoning. A justifiable argument has a strong foundation, meaning that the claims made are supported by rational explanations and valid points. This term reflects clarity in thought and coherence in presenting ideas, which are essential for effective argumentation.

The other choices do not convey this level of credibility. While "controversial" refers to something that may inspire debate or disagreement, it does not imply the soundness of the argument itself. "Unreliable" suggests a lack of dependability or trustworthiness, which contradicts the qualities of a well-reasoned argument. "Flawed" indicates that there are mistakes or weaknesses within the argument, which again detracts from the idea of it being well-reasoned. Thus, "justifiable" stands out as the most fitting descriptor for an argument that is logically sound and defensible.