`a,` Gọi ct chung:\(S_x^{VI}O_y^{II}\)
Theo qui tắc hóa trị: `VI.x=y.II => x/y =` \(\dfrac{II}{VI}\)`= 1/3`
`-> x=1 ; y=3`
`-> CTHH: SO_3`
`b,` Gọi ct chung: \(Al^{III}_x\left(SO_4\right)^{II}_y\)
Theo qui tắc hóa trị: `III.x=y.II => x/y =` \(\dfrac{II}{III}\)` = 2/3`
`-> x=2 ; y=3`
`-> CTHH: Al_2 (SO_4)_3`
`c,` Gọi ct chung: \(Mg^{II}_x\left(CO_3\right)^{II}_y\)
Theo qui tắc hóa trị: `II.x=y.II => x/y =` \(\dfrac{II}{II}\) `= 1`
`-> x=1 ; y=1`
`-> CTHH: MgCO_3`