Which of the following is a national holiday in the United States?

New Year's Day is a national holiday in the United States, celebrated on January 1st each year. It marks the beginning of the new calendar year and is recognized by both federal and state governments, which means that many businesses and schools close on this day. The tradition of celebrating New Year's Day dates back thousands of years, and in the U.S., it is often associated with celebrations that include fireworks, parties, and various cultural customs.

In contrast, Halloween, Valentine's Day, and Earth Day are not recognized as national holidays. Halloween is celebrated on October 31st and has roots in ancient festivals and customs; however, it does not hold the same official status as a national holiday. Valentine's Day, which falls on February 14th, is primarily a cultural and commercial celebration of love and affection, while Earth Day, observed on April 22nd, is focused on environmental protection and awareness. These days may be widely celebrated, but they do not carry the official designation as national holidays like New Year's Day does.