Identify the reaction type

Alkaline $KMnO_4$ at elevated temperature followed by acidification causes oxidative cleavage of the double bond in alkenes.

Write the structure of but-2-ene

But-2-ene is: $CH_3-CH=CH-CH_3$

Apply oxidative cleavage rule

In oxidative cleavage with hot alkaline $KMnO_4$:

• Each carbon of the double bond is converted into a carboxylic acid if it has at least one hydrogen attached.
• If no hydrogen is present, ketone may form.

In but-2-ene, both double-bond carbons are: $-CH=$ So each side has one hydrogen.

Split the molecule across the double bond

$CH_3-CH=CH-CH_3 \rightarrow CH_3COOH + CH_3COOH$

Thus, the products are two molecules of acetic acid.

Check options

• A: one molecule of $CH_3CHO$ and one molecule of $CH_3COOH$ → incorrect
• B: 2 molecules of $CH_3COOH$ → correct
• D: 2 molecules of $CH_3CHO$ → incorrect

Final answer

$\boxed{\text{B: 2 molecules of } CH_3COOH}$