| $MX_\Delta$, $E_rA_r$ (1) | $EA$, $MX_r$ (2) |
| $EX_r$, $M_rA_\Delta$ (3) | $X_rA_r$, $EM$ (4) |
\textbf{201--} Considering the positions of elements $A$, $_{1\Delta}M$, $_{r1}E$, and $_{r\Delta}X$ in the periodic table and their electronic configurations, which compound formed by any two of them is \underline{impossible}?
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\begin{tabular}{ll}
$MX_\Delta$, $E_rA_r$ (1) & $EA$, $MX_r$ (2) \\
$EX_r$, $M_rA_\Delta$ (3) & $X_rA_r$, $EM$ (4)
\end{tabular}
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