\(\left\{{}\begin{matrix}P+N+E=54\\P+N=37\\P=E\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}2P+N=54\\P+N=37\end{matrix}\right.\\ \Leftrightarrow\left\{{}\begin{matrix}P=E=Z=17\\N=20\end{matrix}\right.\\ \Rightarrow A=Z+N=17+20=37\left(đ.v.C\right)\\ \Rightarrow KH:^{37}_{17}Cl\)
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