The smog is essentially caused by the presence of

• A

  $\mathrm{O}_2$ and $\mathrm{O}_3$
• B

  $\mathrm{O}_3$ and $\mathrm{N}_2$
• Correct answer
  C

  Oxides of sulphur and nitrogen
• D

  $\mathrm{O}_2$ and $\mathrm{N}_2$

Hence, the correct answer is option: 'C'.