Final answer:
The reaction of but-2-ene with alkaline KMnO4 and subsequent acidification at elevated temperatures results in the formation of butanoic acid.
Step-by-step explanation:
When but-2-ene reacts with alkaline KMnO4 at elevated temperatures followed by acidification, it undergoes an oxidative cleavage reaction. This process typically oxidizes the double bond to form two separate carbonyl compounds. If the reaction is performed under controlled conditions, it will give butan-2-ol. However, elevated temperatures and a strong oxidizing agent, such as KMnO4, will oxidize the alcohol further, leading to the formation of butanoic acid. Therefore, the correct answer to the question is d. butanoic acid.