Answer
$7.3 \times 10^{21} kg$
Work Step by Step
First, we need to calculate the mass of Earth's crust:
Mass of crust = $ 5.9\times10^{21} tons\times\frac{0.50\% crust}{100 \% Earth} =2.95 \times 10^{19} tons $
The mass of silicon in the crust is then:
Mass of silicon = $ 2.95 \times 10^{19} tons \times\frac{27.2\% Si}{100\% crust} \times \frac{2000 lb}{1 ton} \times\frac{453.6 g}{1 lb} \times\frac{1 kg}{1000 g} = 7.3 \times 10^{21} kg$
