\(CTPT:M_2^a\left(SO_4\right)_3^{II}\\ Theo\cdot QTHT:a.2=II.3\\ \Leftrightarrow a=\frac{II.3}{2}=III\\ \rightarrow M\left(III\right)\\ CTPT:M_x\left(NO_3\right)_y\\ Theo\cdot QTHT:III.x=I.y\\ \Leftrightarrow\frac{x}{y}=\frac{1}{3}\\ \Leftrightarrow\left\{{}\begin{matrix}x=1\\y=3\end{matrix}\right.\\ \rightarrow CTHH:M\left(NO_3\right)_3\)