Final answer:
Louisiana would be most affected by the Mississippi River flooding due to its location in the Mississippi River valley and its past experience with devastating floods like Hurricane Katrina.
Step-by-step explanation:
The state that would be most affected by the Mississippi River flooding is Louisiana. Louisiana is located in the Mississippi River valley, which is prone to flooding due to the river's high water levels. The excerpt mentions that coastal stretches of Alabama, Mississippi, and Louisiana were devastated by Hurricane Katrina, including the city of New Orleans which suffered heavy damage from the failed levees during the storm surge. This event highlights the vulnerability of Louisiana to flooding from the Mississippi River.