Analysis of chlorophyll shows that is containing 2.68 percent magnesium. How many atoms of magnesium does 1.00g of chlorophyll contain?

100g of chlorophyll has =2.68g of Mg

$1 \mathrm{g}\text{ of chlorophyll has }=\frac{1.00\times 2.68}{100} \mathrm{g}\text{ of M}g$

$\begin{array}{l}=\frac{1.00\times 2.68}{100}\times \frac{1}{24} mol\text{ of }\mathrm{mg}\\ =\frac{2.68}{2400}\times 6.02\times {10}^{23}\text{ atoms of }\mathrm{mg}\\ =6.72\times {10}^{20}\text{ atoms }\end{array}$