Contact process reaction conditions

Steps:

• The Contact process involves SO2 production, catalytic oxidation to SO3, and absorption.
• Reaction R's conditions (catalyst, pressure, temperature) match the SO2 to SO3 step except for gas Z.
• Gas Z must be SO2 as the reactant in the oxidation step shown in R.
• Eliminate options by comparing to standard process parameters: V2O5 catalyst, 1-2 atm, 450°C.

Why A is correct:

• In the Contact process, the key gaseous reactant for the catalytic step (R) is SO2, produced earlier from sulfur burning.

Why the others are wrong:

• B: Iron catalyst is incorrect; vanadium(V) oxide (V2O5) is used for SO2 oxidation.
• C: Pressure is 1-2 atm, not 200 atm (which applies to ammonia synthesis).
• D: Temperature is 450°C, not 45°C (too low for the exothermic oxidation).

Final answer: A