The adams-onís treaty established the northern border of spanish territory at the parallel.
a. 49th
b. 36th
c. 42nd
d. 38th

The correct answer is C. The Adams-Onis Treaty established the northern border of Spanish territory at the 42nd parallel.

Explanation:

The Adams-Onis Treaty was an agreement between the United States and Spain in 1819, in which Spain handed over Florida to the United States and defined the boundary between the United States and New Spain (future Mexico) at the 42nd parallel. At the same time, the United States recognized Texas as part of Spain.