Final answer:
The Mississippi River’s significance for transportation and trade was the key factor in the U.S. Congress deciding to admit Louisiana as a state. The correct option is B.
Step-by-step explanation:
The factor that most likely influenced the decision by the U.S. Congress to admit Louisiana as a state was b) The Mississippi River flowed through Louisiana and would lead to increased U.S. transportation and trade. This is evident from the historical context provided, which highlights the importance of the Mississippi River and New Orleans for commerce, trade, and expansion in the North American continent.
Control over the Mississippi River was seen as vital to the interests of the United States, especially after the earlier loss of deposit rights in the port of New Orleans when it was under foreign control.