Which of the following equations represent redox reactions?

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Which of the following equations represent redox reactions?

a. 2KNO3(s)⟶2KNO2(s)+O2(g)
b. H2(g)+CuO(s)⟶Cu(s)+H2O(l)
c. NaOH(aq)+HCl(aq)⟶NaCl(aq)+H2O(l)
d. H2(g)+Cl2(g)⟶2HCl(g)
e. SO3(g)+H2O(l)⟶H2SO4(aq)