Ta có : 2Z+N=58
=> N=58-2Z
Mặc khác : \(Z\le N\le1,5Z\)
=> \(16,6\le Z\le19,3\)
=> \(\left[{}\begin{matrix}Z=17\\Z=18\\Z=19\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}N=24\left(loại\right)\\N=22\left(loại\right)\\N=20\left(chọn\right)\end{matrix}\right.\)
Vậy Z=P=E=19, N=20
Ta có :
\(\left\{{}\begin{matrix}P+N+E=58\\P=E\\P\le1,5N\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}2P+N=58\\P\le N\le1,5P\end{matrix}\right.\\ \Leftrightarrow\left\{{}\begin{matrix}N=58-2P\\P\le58-2P\le1,5P\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}N=58-2P\\3P\le58\le3,5P\end{matrix}\right.\\ \Leftrightarrow\left\{{}\begin{matrix}N=58-2P\\P\le\dfrac{58}{3}\le\dfrac{7}{6}P\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}P=E=Z=19\\N=20\end{matrix}\right.\)
Vậy: Nguyên tử kim loại R có 20n, 19p, 19e. (Kali đó)