The seat of the central (Federal) government is Washington.

Общий вопрос:
Is the seat of the central (Federal) government Washington?

Специальные вопросы:
- к подлежащему
What is Washington?
- к определению при подлежащем
The seat of which government is Washington?

Альтернативный вопрос:
Is the seat of the central (Federal) government Washington or New York?

Разделительный вопрос:
The seat of the central (Federal) government is Washington, isn't it?