One is the only number with letters in reverse alphabetical order.
Forty is the only number whose letters are in alphabetical order.
The King of Hearts is the only king without a mustache.
The letter J is the only letter in the alphabet that does not appear anywhere on the periodic table of the elements.
Queen Isabella I of Spain, who funded Columbus' voyage across the ocean, claimed to have only bathed twice in her life.
Two national capitals are named after U.S. presidents: Washington, D.C., and Monrovia, the capital of Liberia.
John Adams was the only President to be defeated by his Vice President, Thomas Jefferson.
George Washington was the only unanimously elected President.
Maine is the only state with a one-syllable name.
The Valley of Square Trees in Panama is the only known place in the world where trees have rectangular trunks.