Which of the following chemical reactions is an oxidation-reduction (redox) reaction?

• A. $HCl\left(aq\right)$ + $NaOH\left(aq\right)$ → $NaCl\left(aq\right)$ + $H_{2}O\left(l\right)$
• B. $C_2{H}_6\left(g\right)$ → $C_2{H}_4\left(g\right)$ + $H_2\left(g\right)$
• C. $BaC{l}_2\left(aq\right)$ + $N{a}_{2}S{O}_4\left(aq\right)$ → $BaS{O}_4\left(s\right)$ + $2NaCl\left(aq\right)$
• D. $2Mg\left(s\right)$ + $O_2\left(g\right)$ → $2MgO\left(s\right)$

Answer: (D)