b
Maximum enol content is in structure \((b)\) because here the enol form is stabilised by \(H-\) bonding.

\(\underset{\begin{smallmatrix} 
 keto\,\,form \\ 
 (Acetylacetone) 
\end{smallmatrix}}{\mathop{\begin{matrix}
   O\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,O  \\
   ||\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,||  \\
   C{{H}_{3}}-C-C{{H}_{2}}-C-C{{H}_{3}}  \\
\end{matrix}}}\,\) \( \rightleftharpoons \)  \(\mathop {\begin{array}{*{20}{c}}
  {O - H -  - O} \\ 
  {|\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,||} \\ 
  {C{H_3} - C = CH - C - C{H_3}} 
\end{array}}\limits_{enol\,\,form} \)