Question

If ratio of number of molecules of nitrogen to the number of atoms of helium is 1:4 then the ratio of their masses will be?

• A. 1:4
• B. 4:1
• C. 7:4
• D. 6:5

Answer 1

Answer: (C)

7:4

Ratio of number of molecules of nitrogen to the number of atoms of $He$, $N_{N_2}:N_{He}=1:4$

Therefore their mole ratio will be same,

i.e, $n_{N_2}:n_{He}=1:4$

$\Rightarrow \left(\frac{W_{N_2}}{M_{N_2}}\right)/\left(\frac{W_{He}}{M_{He}}\right)=\frac{1}{4}$

$\Rightarrow \frac{W_{N_2}}{14}/\frac{W_{He}}{4}=\frac{1}{4}$

$\Rightarrow \frac{W_{N_2}}{W_{He}}=\frac{1}{4}\times \frac{14}{4}=\frac{7}{4}$

$\therefore$ $W_{N_2}:W_{He}=7:4$

$\therefore$ Correct answer will be C.