At 1 atm and 25°C, a pollutant concentration of 365 µg/m³ corresponds to 139 ppb. Atomic weights are C12,H1,O16,N14,S32. Which pollutant is the closest match?
At 25°C and 1 atm, molar volume is about 24.45 L/mol. For concentration C in µg/m³ and mixing ratio in ppb,$C=ppb\,M/24.45$. Thus molecular weight $M=365(24.45)/139\approx64.2$ g/mol. SO₂ has molecular weight $32+2(16)=64$,while NO₂,O₃ and CO have 46,48 and 28. Hence **A**.
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