Answer
$7.3\times 10^{21}Kg \space Si$
Work Step by Step
We can calculate the mass of silicon in Kilograms as follows:
First of all, we find the mass of crust in tons
$mass \space of \space crust=5.9\times 10^{21}ton\times \frac{0.5}{100}=0.0295\times 10^{21} ton$
Now mass of silicon in tons is given as
$mass \space of \space silicon=0.0295\times 10^{21} \times \frac{27.2}{100}=0.008024\times 10^{21} ton$
mass of silicon in pounds is:
$mass \space of \space silicon=0.008024\times 10^{21}\times 2000lb=16.048\times 10^{21}lb$
It is also given that $1lb=453.6g=\frac{453.6g}{1000}=0.4536Kg$
Finally, we have mass of silicon in Kilograms as given below:
$mass \space of \space silicon=16.048\times 10^{21}\times 0.4536=7.3\times 10^{21}Kg \space Si$
