Which amendment addresses the due process of law?

The 5th Amendment is the correct choice because it explicitly addresses the due process of law. This amendment states that no person shall "be deprived of life, liberty, or property, without due process of law." This means that the government cannot take these fundamental rights away without following fair legal procedures established by law. The concept of due process ensures that individuals have the right to a fair trial, an opportunity to be heard, and legal protections against arbitrary actions by the state.

In contrast, the other amendments mentioned do not specifically address due process. The 3rd Amendment deals with the quartering of soldiers in private homes, the 6th Amendment focuses on the rights of criminal defendants such as the right to a speedy trial and to counsel, and the 9th Amendment recognizes that people's rights are not limited to just those explicitly mentioned in the Constitution. Therefore, while those amendments protect various rights, it is the 5th Amendment that directly pertains to the principle of due process in legal proceedings.