Which of the following catalysts is used in the lead chamber process?

To make huge amounts of sulfuric acid commercially, use the lead chamber process. In this process, ${\mathrm{SO}}_2$ and oxygen react with ${\mathrm{NO}}_2$ to form ${\mathrm{SO}}_3$ as a result of the reaction. In this process, ${\mathrm{NO}}_2$ serves as the catalyst.

$2{\mathrm{SO}}_2+{\mathrm{O}}_2\stackrel{\mathrm{NO}}{\to }2{\mathrm{SO}}_3$