Step 1: Recall the reaction:
Hot or acidic permanganate cleaves alkenes at the double bond and oxidises the pieces. A fragment with an H on the former double-bond carbon becomes an acid.
Step 2: Count carbons:
But-2-ene has four carbons. The double bond sits between C2 and C3, so cleavage splits the chain into two 2-carbon pieces.
Step 3: Identify the piece:
Each 2-carbon piece is $CH_3-CHO$ at first, and further oxidation turns it into $CH_3COOH$.
Step 4: Select:
Two moles of acetic acid form. Only option (B) matches.
Final Answer:
Cleavage at C2-C3 gives two acetic acid molecules.
\[ \boxed{B} \]