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Caffeine has a molecular weight of 194 . If it contains $28.9 \%$ by mass of nitrogen, number of atoms of nitrogen in one molecule of caffeine is
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$4$
$100 \mathrm{gm}$ caffeine has $28.9 \mathrm{gm}$ nitrogen
$\begin{aligned} 194 \mathrm{gm} \text { caffeine has }=\frac{28.9}{100} \times 194 & =56.06 \mathrm{gm} \\ \therefore \quad \text { No. of atoms in } \quad & =\frac{56.06}{14} \approx 4 \text { caffeine }\end{aligned}$
$\begin{aligned} 194 \mathrm{gm} \text { caffeine has }=\frac{28.9}{100} \times 194 & =56.06 \mathrm{gm} \\ \therefore \quad \text { No. of atoms in } \quad & =\frac{56.06}{14} \approx 4 \text { caffeine }\end{aligned}$
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