\textbf{201-} For atom \textbf{a}, the valence electron number is $n+1$ and equals \textbf{m}, and for atom \textbf{b}, the valence electron number is \textbf{x}. The numbers \textbf{a}, \textbf{b}, \textbf{m}, and \textbf{x}, from right to left, can be which of the following?
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(1) $5,5,4,1$ \hspace{2cm} (2) $5,4,4,2$\\[4pt]
(3) $5,4,5,2$ \hspace{2cm} (4) $5,4,5,1$
\end{center}