(i) Suppose oxidation number of Fe in FeSO4 = x
x + 1(-2) = 0
x – 2 = 0
x = +2
∴ Oxidation number of Fe FeSO4 = +2
(ii) Suppose, oxidation number of Fe in Fe(CO)5 = x
x + 5(0) = 0
x + 0 = 0
x = 0
∴ Oxidation number of Fe Fe(CO)5 = 0
(iii) Suppose, oxidation number of P in H3PO3 = x
3(+1) + x + 3(-2) = 0
3 + x – 6 = 0
x – 3 = 0
x = +3
∴ Oxidation number of P in H3PO3 = +3
(iv) Suppose, oxidation number of S in H2S2O7 = x
2(+1) + 2x + 7(-2) = 0
2 + 2x – 14 = 0
2x – 12 = 0
2x = 12
x= \(\frac{12}{2}\) = 6
∴ Oxidation number of S in H2S2O7 = +6
(v) Suppose, oxidation number of C in C12H22O11 = x
12x + 22(+1) + 11(-2) = 0
12x + 22 – 22 = 0
12x + 0 = 0
12x = 0
x = 0
∴ Oxidation number of C in C12H22O11 = 0
(vi) Suppose, oxidation number of C in P in NaH2PO2 = x
1(+1) + 2(+1) + x + 2(-2) = 0
1 + 2 + x – 4 = 0
x – 1 = 0
x = +1
∴ Oxidation number of C in P in NaH2PO2 = +1