d
The enols of \(\beta\) -dicarbonyl compounds are more stable because of conjugation and intramolecular \(H-\) bonding. Thus, the order of stability is

\(\underset{\begin{smallmatrix} 
 (Stabilised\,\,by\,\,conjugation \\ 
 and\,\,H\,-\,bonding )\\ III 
\end{smallmatrix}}{\mathop{\begin{matrix}
   OH\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,O  \\
   |\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,||  \\
   {{H}_{3}}C-C=CH-C-C{{H}_{3}}  \\
\end{matrix}}}\,\) \(>\) \(\mathop {\begin{array}{*{20}{c}}
  {O\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,O} \\ 
  {||\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,||} \\ 
  {C{H_3} - C - C{H_2} - C - C{H_3}} 
\end{array}}\limits_{(II)}\)  \(>\) \(\mathop {\begin{array}{*{20}{c}}
  {OH\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,O} \\ 
  {|\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,||} \\ 
  {C{H_2} = C - C{H_2} - C - C{H_3}} 
\end{array}}\limits_{(I)}\)

Less stable as \((=)\) bond is not in conjugation with carbonyl group.