A keto ester (A) with molecular formula ${{\rm{C}}_6}{{\rm{H}}_{10}}{{\rm{O}}_3}$ on treatment with ${\rm{NaOH}} + {{\rm{I}}_2}$ does not give iodoform but on boiling with dilute $KOH$ gives a compound (B) with molecular formula ${{\rm{C}}_4}{{\rm{H}}_5}{{\rm{O}}_3}{\rm{K}}$ which upon acidification followed by heating undergoes decarboxylation to give acetone. The keto ester (A) is