In a specific gas mixture, the mass ratio of oxygen to nitrogen is 1:4. What is the ratio of the number of molecules of oxygen to nitrogen in this mixture?

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EEJ MAIN Chemistry QUESTION #7185

Question 1

In a specific gas mixture, the mass ratio of oxygen to nitrogen is $1:4$. What is the ratio of the number of molecules of oxygen to nitrogen in this mixture?

$1:8$
$3:16$
$1:4$
$7:32$✔️

Correct Answer Explanation

The number of molecules is proportional to the number of moles ($n = \text{mass} / \text{Molar mass}$):

Let mass of $O_{2} = w$ and mass of $N_{2} = 4w$.
Moles of $O_{2} = w / 32$.
Moles of $N_{2} = 4w / 28 = w / 7$.
Ratio of molecules = $(w/32) : (w/7) = 7 : 32$.

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