Which of the following reactions represents a redox reaction?

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

Answer: (C)

Verified step by step guidance

1. Identify what a redox reaction is: it involves the transfer of electrons between species, resulting in changes in oxidation states of elements.
2. Examine each reaction and assign oxidation states to the elements involved on both sides of the equation.
3. For the reaction \(\mathrm{HCl + NaOH \rightarrow NaCl + H_2O}\), check if any element changes its oxidation state. Here, H, Cl, Na, and O maintain their oxidation states, so this is not a redox reaction.
4. For the reaction \(\mathrm{AgNO_3 + NaCl \rightarrow AgCl + NaNO_3}\), observe that the ions simply exchange partners without changes in oxidation states, indicating no redox process.
5. For the reaction \(\mathrm{2Na + Cl_2 \rightarrow 2NaCl}\), sodium goes from 0 to +1 and chlorine from 0 to -1, showing a clear transfer of electrons and thus a redox reaction.