Which of the following is NOT a national US holiday?

Earth Day is not a national US holiday, making it the correct answer to this question. National holidays are designated by federal law, and they are officially recognized days when federal employees are given the day off, and various public observances may take place. Thanksgiving, Independence Day, and Labor Day are all established national holidays in the United States.

Thanksgiving is celebrated on the fourth Thursday of November and has historical roots connected to the harvest festivals of the early 1600s. Independence Day, celebrated on July 4th, commemorates the adoption of the Declaration of Independence in 1776. Labor Day, observed on the first Monday in September, honors the American labor movement and the contributions of workers.

In contrast, Earth Day, marked on April 22nd, focuses on environmental awareness and protection but does not hold the status of a federally recognized holiday. Thus, it does not provide the same benefits or recognitions as the other holidays mentioned.