Oxidation State ?

Consider the reaction: C₆H₁₂O₆(s) + 6O₂(g) → 6CO₂(g) + 6H₂O(g)

Oxidation states of elements in the reactants:
H in C₆H₁₂O₆ = +1
O in C₆H₁₂O₆ = -2
C in C₆H₁₂O₆ = [0 - 12(+1) - 6(-2)]/6 = 0
O in O₂ = 0

Oxidation states of elements in the products:
O in CO₂ = -2
C in CO₂ = 0 - 2(-2) = +4
H in H₂O = +1
O in H₂O = -2

C (in C₆H₁₂O₆) is oxidized because the oxidation state of C increases from 0 to +4 (in CO₂).
O (in O₂) is reduced because the oxidation state of O decreases from 0 to -2 (in CO₂ and H₂O).

====
Consider the following reaction: C₂H₄(g) + Cl₂(g) → C₂H₄Cl₂(g)

Oxidation states of the elements in the reactants:
H in C₂H₄ = +1
C in C₂H₄ = [0 - 4(+1)]/2 = -2
Cl in Cl₂ = 0

Oxidation states of the elements in the product:
H in C₂H₄Cl₂ = +1
Cl in C₂H₄Cl₂ = -1
C in C₂H₄Cl₂ = [0 - 4(+1) - 2(-1)]/2 = -1

C is oxidized because the oxidation state of C increases from -2 (in C₂H₄) to -1(in C₂H₄Cl₂).
Cl is reduced because the oxidation state of C decreases from 0 (in Cl₂) to -1 (in C₂H₄Cl₂).