What is the only US state that begins with the letter F?

Yes 18 sovereign states start with B:

Bahamas

Bahrain

Bangladesh

Barbados

Belarus

Belgium

Belize

Benin

Bhutan

Bolivia

Bosnia and Herzegovina

Botswana

Brazil

Brunei

Bulgaria

Burkina Faso

Burma* (officially changed to Myanmar, but some countries still call it Burma)

Burundi