Which of the following balanced equations represents a redox (oxidation-reduction) reaction?

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

Answer: (B)

Verified step by step guidance

1. Step 1: Understand what a redox reaction is. A redox (oxidation-reduction) reaction involves the transfer of electrons between species, resulting in changes in oxidation states of elements.
2. Step 2: Examine each equation and identify if there is a change in oxidation states of any element from reactants to products.
3. Step 3: For the equation \(\mathrm{CaCO_3 \rightarrow CaO + CO_2}\), check the oxidation states of calcium, carbon, and oxygen on both sides to see if any element is oxidized or reduced.
4. Step 4: For the equation \(\mathrm{2Na + Cl_2 \rightarrow 2NaCl}\), determine the oxidation states of sodium and chlorine before and after the reaction to see if electron transfer occurs.
5. Step 5: For the other equations, \(\mathrm{AgNO_3 + NaCl \rightarrow AgCl + NaNO_3}\) and \(\mathrm{HCl + NaOH \rightarrow NaCl + H_2O}\), analyze if any oxidation state changes occur, indicating redox, or if they are simply double displacement or acid-base neutralization reactions.