Which One of the Following Is an Oxidation-Reduction Reaction?
A) $\rightarrow$

Which one of the following is an oxidation-reduction reaction?

A) CaCO₃ (s) $\rightarrow$ CaO (s) + CO₂
B) CaO (s) + 2 HCl (aq) $\rightarrow$ CaCl₂ (aq) + H₂O (l)
C) 2 KNO₃ (s) $\rightarrow$ 2 KNO₂ (s) + O₂ (g)
D) HCl (aq) + NaOH (aq) $\rightarrow$ NaCl (aq) + H₂O (l)
E) none of these