1.
a, `Na(I) ; SO4(II)` `CT:Na_a(SO_4)_b`
Ta có : `a.1 = b.2 => a/b = 2/1`
`=> CT : Na_2SO_4`
b, `S (VI) ; O (II)` . `CT: S_aO_b`
Ta có : `a.6=b.2 => a/b = 2/6=1/3`
`=> CT : SO_3`
2.
`%Cu = (M_(Cu))/(M_(CuO))=(64)/(64+16).100=80%`
`=> %O = 100% -80% =20%``
3.
1. `4P + 5O2 -> 2P2O5`
2. `Fe + 2HCl -> FeCl2 + H2`
3. `3Fe + 2O2 -> Fe3O4`
4. `CT: Fe_xO_y`
`%Fe =70%`
`<=> (M_(Fe).x)/(M_(Fe_xO_y)).100=70%`
`<=> (56.x)/(160).100=70%``
`=> 56.x= 160.70%=112`
`=> x= (112)/(56)=2`
`M_(Fe_xO_y)=56.x+16.y`
`<=> 160 = 56.2 + 16.y`
`<=> 160 = 112 + 16.y`
`=> y = 3`
`=> CT : Fe_2O_3`
