The gas that can be dried using concentrated tetraoxosulphate(VI) acid (H2SO4) must not react with it. Concentrated H2SO4 is a strong acid, an oxidizing agent, and a dehydrating agent.
Let's examine each option:
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A) Hydrogen bromide (HBr): HBr is a reducing agent. Concentrated H2SO4 will oxidize HBr to bromine (Br2).
2HBr+H2SO4→Br2+SO2+2H2O
Therefore, HBr cannot be dried by concentrated H2SO4.
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B) Sulphur(IV) oxide (SO2): SO2 is an acidic gas. It does not react with concentrated H2SO4 because both are acidic.
Therefore, SO2 can be dried by concentrated H2SO4.
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C) Hydrogen sulphide (H2S): H2S is a strong reducing agent. Concentrated H2SO4 will oxidize H2S to sulfur (S).
H2S+H2SO4→S+SO2+2H2O
Therefore, H2S cannot be dried by concentrated H2SO4.
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D) Ammonia (NH3): NH3 is a basic gas. It will react with the acidic concentrated H2SO4 to form ammonium sulfate.
2NH3+H2SO4→(NH4)2SO4
Therefore, NH3 cannot be dried by concentrated H2SO4.
Based on this analysis, only sulphur(IV) oxide can be dried using concentrated tetraoxosulphate(VI) acid.
The final answer is B.