Identify the product obtained when alkenes are oxidised with $\mathrm{KMnO}_4$ in dil. $\mathrm{H}_2 \mathrm{SO}_4$.

Strong oxidative cleavage of alkenes with potassium permanganate in dilute sulfuric acid cleaves carbon-carbon double bonds. The products depend on substitution patterns: vinylic carbons with hydrogen atoms oxidize to carboxylic acids (alkanoic acids), while fully substituted vinylic carbons oxidize to ketones (alkanones).

Under these strongly oxidizing conditions, alkanals (aldehydes) are unstable intermediates that undergo further oxidation to carboxylic acids. Alkanols are not formed, as they result from milder oxidation conditions. While both alkanones and alkanoic acids may be produced depending on substrate structure, alkanoic acids represent the most general and stable oxidation product.

The correct answer is $\boxed{\text{D}}$.