Question

Which is a formal region?
(Points : 1)
The state of Illinois

The Chicago metropolitan area

The historic neighborhoods in Boston

The trade route along the Mississippi River

Answer 1

formal means official or recognized 

so the best answer would be the state of Illinois, the others are general areas

Answer 2

The State of Illinois is a formal region, with a sharply defined boundary.
In principle, with careful enough measurement, you can always find
exactly where any place on its boundary is, and you can stand there
with one foot inside Illinois and one foot outside of it.  I have done this
many times.