The correct option is A 1.4 ppm
SO2+H2O→H2SO3
2MnO−4+5H2SO3→2Mn2++3H2O+5SO2−4+4H+
2 moles MnO−4=5 moles of H2SO3 or SO2
2.5×10−5 moles MnO−4=52×2.5×10−5 moles SO2
=6.25×10−5 moles SO2
At S.T.P, 6.25×10−5 moles=6.25×10−5×22.4 L SO2
=1.4×10−3L
In 1000 L air, SO2=1.4×10−3L
In 106L,SO2=1.4×10−3×10610−3=1.4 ppm