`2.`
` a, Ba(II); OH (I) : CT: Ba(OH)2`
` b, Al(III); NO3(I) : CT : Al(NO3)3`
` c, Cu(II); CO3 (II) : CT : Cu2(CO3)2` tối giản `CuCO3`
` d, Fe(II); O(II) : CT : Fe2O2` tối giản` FeO`
`3. A` có hoá trị `a; B` có hoá trị `b ; CT: AxBy`
Ta có `: a.x = b.y`
` FeSO4 : a.1=2.1 => a=2 => Fe(II)`
` Al2O3: a.2=2.3 => a=3 => Al(III)`
` Al2(SO4)3 : a.2=2.3 => a=3 => Al(III)`
`4.`
` a, N : H = (82,35%)/14 : (17,65%)/1`
`= 0,0588 :0,1765`
`= 1:3`
` => CT : NH3`
` b, H : S : O = (2,04%)/1 : (32,65%)/32 : (65,306%)/16`
` = 2 : 1 : 4`
` => CT : H2SO4`
` c, % O = 42,11%`
` Fe : S : O = (36,84%)/56 : (21,05%)/32 : (42,11%)/16`
` = 0,00657 : 0,00657 : 0,0263`
` = 1 : 1 : 4`
` => CT : FeSO4`
