(i) S in `H_(2)SO_(4)`
Let the oxidation number of s in `H_(2)SO_(4)` be x
Write the oxidation number of each atom above its symbol
`H_(2)^(+1) overset(x)S O_(4)^(-2)`
Calculate the sum of the oxidation numbers of all the atoms
Since `H_(2)SO_(4)` is a neutral molecule, the sum of oxidation numbers must be zero.
(ii) S in `Na_(2)SO_(4)`
Let the oxidation number of S in `Na_(2)SO_(4)` be x
Write the oxidation number of each atom above its symbol
`overset(+1)Na_(2) overset(x)S overset(-2)O_(4)`
Calculate the sum of the loxidation numbers of all the atoms
2(+1) +x+4(-2)=2+x-8=x-6
since `Na_(2)SO_(4)` is a neutral molecule, the sum of the oxidation numbers must be zero
x-6=0 or x=+6
(iii) S in `SO_(4)^(2)` ion
Let the oxidation number of S in `SO_(4)^(2)` ion be x
write the oxidatioin numbers of both the atoms above their symbols
calculate the sum of the oxidation numbers of both the atoms
`x+4(-2)=x-8`
Since `SO_(4)^(2)` ion is an anion the sum of the oxidation numbers must be -2
x-8=-2 or x= -2+=+6
(iv) S in `S_(2)O_(4)^(2)`ion
“Let the oxidation number of S in `S_(2)O_(4)^(2)` ion be x.
Write the oxidation numbers of both atoms above their symbols”
`overset(x)S_(2) overset(-2)O_(4)`
“Calculate the sum of oxidation number of both the atoms”
`2(x)+4(-2)=2x-8`
Since `S_(2)O_(4)^(2)` “is an anion the sum of the oxidation numbers must be” -2
`2(x) -8=-2 or 2 x =- 2 + 8 = 6 or x =6//2 =+3`