Which of the following is an example of a state in the United States?

Texas is an example of a state in the United States because it is one of the 50 states that form the country. Each state has its own government, laws, and regulations, but they are all part of the larger federal system of the U.S. Texas, specifically, is known for its significant size, diverse geography, and distinct cultural identity. It plays a vital role in various aspects such as economy, sports, and history within the U.S.

The other options do not fit the criteria of a U.S. state: Ontario and Canada are locations in Canada, while Mexico is a separate country entirely. Thus, Texas distinctly stands out as the correct answer in this context.