b
$\begin{matrix}
C{{H}_{3}} \\
C{{H}_{3}} \\
\end{matrix}>\,C\,=\,O\,+\,C{{H}_{3}}C{{H}_{2}}MgBr\,\to $ $\begin{matrix}
C{{H}_{3}} \\
C{{H}_{3}} \\
\end{matrix}>\,C\,<\,\begin{matrix}
OMgBr \\
C{{H}_{2}}C{{H}_{3}} \\
\end{matrix}\,\xrightarrow{{{H}_{2}}O}$ $\underset{\begin{smallmatrix}
2\,\,methyl\,\,bu\tan ol\,\,-\,2 \\
\,\,\,\,\,\,\,({{3}^{o}}\,\,alcohol)
\end{smallmatrix}}{\mathop{\begin{matrix}
C{{H}_{3}} \\
C{{H}_{3}} \\
\end{matrix}>\,C\,<\,\begin{matrix}
OH \\
C{{H}_{2}}C{{H}_{3}} \\
\end{matrix}}}\,$