(a) \begin{tikzpicture}[scale=0.8]
\draw (0,0) -- (1,0) -- (1,1) -- (0,1) -- cycle;
\draw (1,1) -- (2,1.5);
\draw (2,1.5) -- (3,1.5);
\draw (3,1.5) node[right] {Br};
\draw (1.5,0.5) -- (1.5,1.5);
\draw[->] (3.5,1.2) -- (4.5,1.2);
\draw (4,1.2) node[above] {$H_2O$};
\draw (5,1.2) node[right] {?};
\end{tikzpicture}
(b) \begin{tikzpicture}[scale=0.8]
\draw (0,0) -- (1,0) -- (1,1) -- (0,1) -- cycle;
\draw (1,1) -- (2,1.5);
\draw (2,1.5) -- (3,1.5);
\draw (3,1.5) node[right] {Br};
\draw (1.5,0.5) -- (1.5,1.5);
\draw[->] (3.5,1.2) -- (4.5,1.2);
\draw (4,1.2) node[above] {$-OH$};
\draw (5,1.2) node[right] {?};
\end{tikzpicture}
