In the diagram below, the purpose of the asbestos to

Correct answer: catalyse the reaction.

Why: The packed bed is platinized asbestos—asbestos serves as a support for finely dispersed Pt, which catalyzes the oxidation

\(\mathrm{SO_2(g) + \tfrac12\,O_2(g) \rightarrow SO_3(g)}\)

by lowering the activation energy (Contact-process step).

• Absorb impurities — Not its role here.
• Solidify the gas — The freezing mixture/receiver handles condensation, not the catalyst bed.
• Dry the gas — Drying is done with conc. H₂SO₄, not the asbestos support.