Answer
Molar mass of PbS = $239.3\,g/mol$
Mass percent of Pb= $86.60\%$
Mass percent of S= $13.40\%$
Work Step by Step
Molar mass of PbS=
Molar mass of Pb+ Molar mass of S
$=207.2\,g/mol+ 32.065\,g/mol$
$= 239.3\,g/mol$
Mass percent of Pb=$ \frac{207.2\,g}{239.265\,g}\times100\%$
$=86.60\%$
Mass percent of S= $\frac{32.065\,g}{239.265\,g}\times 100\%$
$=13.40\%$
