\(\%m_O=\dfrac{1}{5}=20\%\left(=\dfrac{1}{4}\cdot80\%\right)\\ 0,2=\dfrac{16n}{2B+16n}\\ 0,4B+3,2n=16n\\ B=32n\\ n=2;B=64\left(Cu\right)\\ HC:CuO\)
`\%m_O=1/{4}.100\%=25\%`
`->{16n}/{2B+16n}.100=25`
`->2B+16n=64n`
`->B=24n`
Không có nguyên tố thỏa mãn.