JEE Advanced levelSingle correct optionDifficulty 3 of 3ev047
A 250 L sample of air measured at STP contains 1.10 mg of SOX2 (assume ideal gas, molar volume 22.4 L/mol at STP, S=32, O=16). The concentration of SOX2 in ppm by volume is
A4.40 ppm
B1.54 ppm
C15.4 ppm
D0.0154 ppm
Answer: B
Moles of SOX2 = 1.10×10−3/64=1.72×10−5 mol, occupying 1.72×10−5×22.4=3.85×10−4 L. ppm by volume = 3.85×10−4/250×106=1.54. The value 4.40 is just mass per volume in mgm−3.