Sulphuric acid is manufactured by the contact process. Which step is not involved in the process?

Burning of sulphur of sulphide ores in air to generate ${\mathrm{SO}}_2$

The ${\mathrm{SO}}_2$ produced is purified by removing dust and other impurities such as arsenic compounds.

Conversion of ${\mathrm{SO}}_3$  to ${\mathrm{SO}}_2$ in the presence of a catalyst $\left({\mathrm{V}}_2{\mathrm{O}}_5\right)$

Absorption of ${\mathrm{SO}}_3$ in ${\mathrm{H}}_2{\mathrm{SO}}_4$ to give oleum $\left({\mathrm{H}}_2{\mathrm{S}}_2{\mathrm{O}}_7\right)$