Which balanced equation represents a redox reaction (i.e., involves a change in oxidation numbers)?

• A. $H\mathrm{Cl}$(aq) $+$ $\mathrm{Na}OH$(aq) $\to$ $\mathrm{Na}\mathrm{Cl}$(aq) $+$ $H_{2}O$(l)
• B. ${\mathrm{Na}}_{2}C{O}_3$(aq) $+$ ${\mathrm{Ca}}_{\mathrm{Cl}}{O}_2$(aq) $\to$ ${\mathrm{Ca}}_{1}C{O}_3$(s) $+$ $2\mathrm{Na}\mathrm{Cl}$(aq)
• C. $H_2$(g) $+$ ${\mathrm{Cl}}_2$(g) $\to$ $2H\mathrm{Cl}$(g)
• D. ${\mathrm{Zn}}_1$(s) $+$ ${\mathrm{Cu}}_1{S}_O{O}_4$(aq) $\to$ ${\mathrm{Zn}}_1{S}_O{O}_4$(aq) $+$ ${\mathrm{Cu}}_1$(s)

Answer: (D)