Step 1: Understanding the Concept
Acidified KMnO\(_4\) is a strong oxidant. It breaks the double bond completely, and any aldehyde formed is oxidised further.
Step 2: Detailed Explanation
The alkene splits into two fragments at the double bond. A \(=\text{CH}_2\) end becomes CO\(_2\), and a \(=\text{CHR}\) end becomes RCOOH.
Since aldehydes cannot survive the oxidising medium, they go on to the carboxylic acid.
The class of product asked in the question is alkanoic acid.
Final Answer:
Alkenes give carboxylic acids (alkanoic acids), option (D).
\[ \boxed{\text{Alkanoic acid (D)}} \]