\textbf{178.} Four charged particles are placed at the vertices of a square. The electric forces on the charged particle $q_2$ are zero. What is $\dfrac{Q}{q}$?
\begin{minipage}{0.4\textwidth}
\textit{[Figure: Square with charges at vertices: $q_1 = q$ (top-left), $q_2 = Q$ (top-right), $q_3 = q$ (bottom-right), $q_4 = -\dfrac{1}{2}Q$ (bottom-left).]}
\end{minipage}
\hfill
\begin{minipage}{0.5\textwidth}
\begin{itemize}
\item[(1)] $2\sqrt{2}$
\item[(2)] $4\sqrt{2}$
\item[(3)] $-2\sqrt{2}$
\item[(4)] $-4\sqrt{2}$
\end{itemize}
\end{minipage}
\vspace{1em}