Which of the following is a national holiday in the U.S.?

New Year's Day is recognized as a national holiday in the United States, celebrated on January 1st each year. It marks the beginning of the new calendar year and is observed with various traditions, including celebrations and fireworks in many cities across the country.

In contrast, Flag Day, while important and recognized in certain states, is not a national holiday and does not require a day off for federal employees. Halloween is a widely celebrated cultural event on October 31st, but it is not officially designated as a national holiday. Similarly, Earth Day, celebrated on April 22nd, raises awareness about environmental issues but is also not classified as a national holiday in the U.S.