Question

Caffeine has a molecular weight of $194$. It contains $28.9$% by mass of nitrogen. Number of atoms of nitrogen in one molecule of it is:

• A. $2$
• B. $3$
• C. $4$
• D. $5$

Answer 1

Answer: (C)

$4$

$100$ g of Caffeine contains $=28.9$ g of $N$.

$\therefore 194$ g of Caffeine contains $=\frac{28.9}{100}\times 194$ g $=56$ g.

Number of moles of $N$ $=\frac{56}{14}=4$

The number of atoms of $N$ is one molecule is $4$.