Calculate the oxidation number of 

(i) S in H₂S

(ii) C in CO₂

(iii) C in CH₂Cl₂

(iv) N is (NH₄)₂SO₄

(v) Pb in Pb₃O₄

(vi) P in Na₃PO₄

(i) S in H₂S
      Let oxidation number of S = x.
      2(+1) + x = 0 ⟶ x = −2
      Oxidation number of S = −2

(ii) C in CO₂
       Let oxidation number of C = x.
       x + 2(−2) = 0 ⟶ x = +4
       Oxidation number of C = +4

(iii) C in CH₂Cl₂
        Let oxidation number of C = x.
        x + 2(+1) + 2(−1) = x = 0
       Oxidation number of C = 0

(iv) N in (NH₄)₂SO₄
        Let oxidation number of N = x.
        2x + 8(+1) + (−2) = 2x + 6 = 0 ⟶ x = −3
        Oxidation number of N = −3

(v) Pb in Pb₃O₄
       Let oxidation number of Pb = x.
       3x + 4(−2) = 0 ⟶ 3x − 8 = 0 ⟶ x = 8/3
       Oxidation number of Pb = 8/3

(vi) P in Na₃PO₄
        Let oxidation number of P = x.
        3(+1) + x + 4(−2) = x − 5 = 0 ⟶ x = +5
        Oxidation number of P = +5