Q17 / 120 · VITEEE 2015 · Chemistry

Caffeine has a molecular weight of $194 \mathrm{u}$. If it contains $28.9 \%$ by mass of nitrogen, number of atom of nitrogen in one molecule of caffeine is

  • Correct answer
    A
    4
  • B
    6
  • C
    2
  • D
    3

Solution

M.wt. of caffeine $=194 \mathrm{u}$ $\%$ of $\mathrm{N}$ present in one molecular of caffeine is $28.9 \%$ of $194 u=\frac{28.9}{100} \times 194=56 u$ Mass of one $\mathrm{N}$ atom $=14 \mathrm{~m}$ $=1 \mathrm{~N}$ atom $\quad(\because 14 \mathrm{~m}=14 \mathrm{u})$ $\therefore \quad 56 \mathrm{u}=\frac{56}{14} \mathrm{~N}$ atom $=4 \mathrm{~N}$ atom

Hence, the correct answer is option: 'A'.

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