Which amendment to the Constitution officially abolished slavery in the United States?

The 13th amendment to the Constitution is the correct answer because it specifically addresses the prohibition of slavery and involuntary servitude in the United States. Ratified in December 1865, this amendment states that neither slavery nor involuntary servitude, except as a punishment for a crime, shall exist within the United States, thereby officially abolishing the legal practice of slavery.

The other amendments listed do not pertain to the abolition of slavery. The 12th amendment addresses the election of the President and Vice President, the 14th amendment grants citizenship rights and equal protection under the law to all persons born or naturalized in the United States, and the 15th amendment prohibits the denial of the right to vote based on race, color, or previous condition of servitude. Each of these amendments serves important functions in expanding rights and protections, but it is the 13th amendment that directly ended the institution of slavery.