b
\(2, 4-\)hexanedione (a \(1, 3-\)diketone) has the most acidic hydrogen. This is because the carbanion left after the removal of \({H^ + }\) is resonance stabilised in this case.

\(\mathop {C{H_3} - \mathop {\mathop C\limits^{||} }\limits^O  - C{H_2} - \mathop {\mathop C\limits^{||} }\limits^O  - C{H_2}C{H_3}}\limits_{2,\,4 - {\text{Hexanedione}}} \mathop {\xrightarrow{{O{H^ - }}}}\limits_{ - {H_2}O} \)   \(C{H_3} - \mathop {\mathop C\limits^{||} }\limits^O \, - \mathop C\limits^ -  H - \mathop {\mathop C\limits^{||} }\limits^O  - C{H_2}C{H_3}\) 

 \(C{H_3} - \mathop {\mathop C\limits^{||} }\limits^O  - \mathop C\limits^ -  H - \mathop {\mathop C\limits^{||} }\limits^O  - C{H_2}C{H_3}\)   \( \leftrightarrow C{H_3} - \mathop {\mathop {C\,\,}\limits^{|\,\,\,\,} }\limits^{{O^ - }}  = CH - \mathop {\mathop C\limits^{||} }\limits^O  - C{H_2}C{H_3}\)    \( \leftrightarrow C{H_3} - \mathop {\mathop {C\,\,}\limits^{||\,\,\,\,} }\limits^{O\,\,}  - CH = \mathop {\mathop {C\,\,}\limits^{|\,\,\,\,} }\limits^{{O^ - }}  - C{H_2}C{H_3}\)