Question

add a comma or semicolon if needed. otherwise, submit the text without any additional punctuation.
airplane food has a reputation for being unappetizing square but the food itself may not be responsible. researchers have discovered that high altitude and decreased humidity dull our ability to detect flavors.

Explanation:

The two independent clauses "Airplane food has a reputation for being unappetizing" and "but the food itself may not be responsible" are connected by the coordinating conjunction "but". When a coordinating conjunction (for, and, nor, but, or, yet, so) connects two independent clauses, a comma is used before the conjunction. So we add a comma before "but".

Answer:

Airplane food has a reputation for being unappetizing, but the food itself may not be responsible. Researchers have discovered that high altitude and decreased humidity dull our ability to detect flavors.