Which of the following chemical equations represents a redox reaction?

• A. CaCO_3 → CaO + CO_2
• B. 2Na + Cl_2 → 2NaCl
• C. AgNO_3 + NaCl → AgCl + NaNO_3
• D. H_2SO_4 + NaOH → Na_2SO_4 + H_2O

Answer: (B)

Verified step by step guidance

1. Identify what a redox reaction is: it involves the transfer of electrons, meaning one species is oxidized (loses electrons) and another is reduced (gains electrons).
2. Examine each equation to see if there is a change in oxidation states of elements from reactants to products.
3. For the equation \(\mathrm{CaCO_3 \rightarrow CaO + CO_2}\), check the oxidation states of calcium, carbon, and oxygen to see if any change occurs.
4. For the equation \(\mathrm{2Na + Cl_2 \rightarrow 2NaCl}\), determine the oxidation states of sodium and chlorine before and after the reaction to identify electron transfer.
5. For the other equations, \(\mathrm{AgNO_3 + NaCl \rightarrow AgCl + NaNO_3}\) and \(\mathrm{H_2SO_4 + NaOH \rightarrow Na_2SO_4 + H_2O}\), verify if any oxidation state changes occur to confirm if they are redox or not.