\(\text{Đ}\text{ặt}:Cu_a^{II}O_b^{II}\left(a,b:nguy\text{ê}n,d\text{ươ}ng\right)\\ QTHT:a.II=b.II\Leftrightarrow\dfrac{a}{b}=\dfrac{II}{II}=\dfrac{2}{2}=\dfrac{1}{1}\Rightarrow a=1;b=1\\ \Rightarrow CTHH:CuO\\ \text{Đ}\text{ặt}:Fe_m^{III}\left(SO_4\right)_n^{II}\left(m,n:nguy\text{ên},d\text{ươ}ng\right)\\ QTHT:m.III=n.II\\ \Leftrightarrow\dfrac{m}{n}=\dfrac{II}{III}=\dfrac{2}{3}\\ \Rightarrow m=2;n=3\\ \Rightarrow CTHH:Fe_2\left(SO_4\right)_3\)