10.0dm³ of air containing H₂S as an impurity was passed through a solution of Pb(NO₃)₂ until all the H₂S had reacted. The precipitate of PbS was found to weigh 5.02g. According to the equation,
Pb (NO₃)2 + H₂S ---> PbS + HNO₂ the percentage by volume of hydrogen sulphide.
(Pb = 207, s = 32, GMV at STP = 22.4dm³)

• A.50.2
• B.47.0
• C.4.70
• D.0.47