Which of the following reactions would be classified as an oxidation-reduction (redox) reaction?

• A. 2Na + Cl_2 ightarrow 2NaCl
• B. CaCO_3 ightarrow CaO + CO_2
• C. HCl + NaOH ightarrow NaCl + H_2O
• D. AgNO_3 + NaCl ightarrow AgCl + NaNO_3

Answer: (A)

Verified step by step guidance

1. Step 1: Understand that an oxidation-reduction (redox) reaction involves the transfer of electrons, which means one species is oxidized (loses electrons) and another is reduced (gains electrons).
2. Step 2: Analyze each reaction by assigning oxidation states to the elements involved to see if there is a change in oxidation numbers from reactants to products.
3. Step 3: For the reaction \$2Na + Cl_2 \rightarrow 2NaCl$, assign oxidation states: Na goes from 0 to +1, Cl goes from 0 to -1, indicating electron transfer, so this is a redox reaction.
4. Step 4: For the reaction \(CaCO_3 \rightarrow CaO + CO_2\), check oxidation states: Ca remains +2, C remains +4, and O remains -2, so no change in oxidation states, meaning it is not a redox reaction but a decomposition.
5. Step 5: For the reactions \(HCl + NaOH \rightarrow NaCl + H_2O\) and \(AgNO_3 + NaCl \rightarrow AgCl + NaNO_3\), verify oxidation states remain constant, indicating these are acid-base neutralization and double displacement reactions, respectively, not redox.