a
$(a)$ ${{C}_{6}}{{H}_{5}}COO{{C}_{2}}{{H}_{5}}\,\xrightarrow{C{{H}_{3}}MgBr}$ $\begin{matrix}
\begin{matrix}
\,\,\,\,\,\,\,\,\,\,\,\,OMgBr \\
| \\
\end{matrix}\,\,\,\, \\
{{C}_{6}}{{H}_{5}}-C-O{{C}_{2}}{{H}_{5}} \\
|\,\,\,\, \\
\,\,C{{H}_{3}} \\
\end{matrix}$ $\xrightarrow{-\,Mg\,(O{{C}_{2}}{{H}_{5}})Br}$ $\begin{matrix}
\,O \\
\,\,|| \\
{{C}_{6}}{{H}_{5}}-C-C{{H}_{3}} \\
\end{matrix}$ $\xrightarrow[C{{H}_{3}}MgBr]{Excess}$ $\begin{matrix}
\begin{matrix}
\,\,\,\,\,\,\,\,\,\,\,\,OMgBr \\
| \\
\end{matrix}\,\,\,\, \\
{{C}_{6}}{{H}_{5}}-C-OC{{H}_{3}} \\
|\,\,\,\, \\
\,\,C{{H}_{3}} \\
\end{matrix}$ $\xrightarrow{{{H}_{2}}O}$ $\begin{matrix}
\begin{matrix}
\,\,\,\,\,\,\,\,\,\,\,\,\,\,C{{H}_{3}}\,\,\,\, \\
\,\,\,\,| \\
\end{matrix}\,\,\,\, \\
{{C}_{6}}{{H}_{5}}-C-C{{H}_{3}} \\
\,\,\,\,\,|\,\,\,\, \\
\,\,\,\,\,\,\,OH \\
\end{matrix}$ $\xrightarrow[\Delta ]{Conc.\,{{H}_{2}}S{{O}_{4}}}$ $\begin{matrix}
\,\,\,\,\,C{{H}_{3}} \\
| \\
{{C}_{6}}{{H}_{2}}-C=C{{H}_{2}} \\
\end{matrix}$ $\xrightarrow{Ozonolysis}$ $\overset{'B'}{\mathop{{{C}_{6}}{{H}_{5}}COC{{H}_{3}}\,+\,HCHO}}\,\,$
${\mathop{{{C}_{6}}{{H}_{5}}COC{{H}_{3}}\,\xrightarrow{3{{I}_{2}}\,+\,4NaOH}\,CH{{I}_{3}}}}\,\,$