| (1) 3 | (2) 4 | (3) 5 | (4) 6 |
\textbf{206--} How many of the following ionic compound formulas are correct?
\begin{itemize}
\item Magnesium nitride: $Mg_rN_r$ \hfill Gallium chloride: $GaCl_r$
\item Copper(II) sulfide: $Cu_rS$ \hfill Cobalt(III) sulfate: $CO_r(SO_f)_r$
\item Barium cyanide: $Ba(CN)_r$ \hfill Zinc phosphate: $Zn_r(PO_f)_r$
\end{itemize}
\begin{tabular}{llll}
(1) 3 & (2) 4 & (3) 5 & (4) 6
\end{tabular}
\medskip