What fraction of states must approve an amendment for it to become part of the U.S. Constitution?

In order for an amendment to become part of the U.S. Constitution, it must be ratified by three-fourths of the state legislatures or by conventions in three-fourths of the states. This process is outlined in Article V of the Constitution, which establishes the procedures for amending the document.

The requirement for three-fourths approval ensures that a significant majority of states agree to the proposed changes, reflecting a broad consensus across the country. This high threshold serves to prevent hasty changes to the Constitution, emphasizing stability and careful consideration of any amendments. Given the United States' federal structure, this requirement helps to balance the interests of various states and maintain national unity.

The other options, such as one-half, two-thirds, and one-third, do not represent the necessary consensus needed for constitutional amendments, which would make their approval insufficient and could lead to instability in governance.