\(a,\\ \left\{{}\begin{matrix}P+N+E=46\\P=E=Z\\N=16\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}2P+N=46\\N=16\end{matrix}\right.\\ \Leftrightarrow\left\{{}\begin{matrix}P=E=Z=15\\N=16\end{matrix}\right.\\ b,m_O=0,16605.10^{-23}.16=2,6568.10^{-23}\left(g\right)\)