In which century did George Washington serve as President?

George Washington served as the President of the United States from 1789 to 1797, which falls squarely within the 18th century. The 18th century spans the years 1701 to 1800, making it the appropriate time frame for Washington's presidency. This era was critical in shaping the early government of the United States following its independence from Britain. The establishment of the executive role that Washington filled helped set many precedents for future presidents, such as the importance of serving only two terms.

In contrast, the other centuries listed do not correspond to Washington's presidency. The 17th century encompasses the years 1601 to 1700, well before the United States was established. The 19th century, which spans from 1801 to 1900, occurs after Washington's time in office, while the 20th century covers the years 1901 to 2000, significantly later than his presidency. Thus, the correct choice reflects the historical context of Washington's leadership in the late 1700s.