Question

Four one-liter flasks are separately filled with the gases ${ O }_{ 2 }$, ${ F }_{ 2 }$, ${ CH }_{ 4 }$ and ${ CO }_{ 2 }$ under the same conditions.
The ratio of the number of molecules in these gases are:
A. 2:2:4:3
B. 1:1:1:1
C. 1:2:3:4
D. 2:2:3:4

Answer 1

Hint: You should focus on the words “under the same conditions”. Now, just recall laws related to gases from the kinetic theory of gases. Also, remember the answer has nothing to do with the molecular weight of gases. Now, you can easily answer this question.

Complete step by step answer:

First, let’s know about the law we are going to apply here-
Avogadro's law: It states that equal volumes of gases at the same temperature and pressure contain equal numbers of molecules.
So, Volume = V, then n1 =n2 =n3 = n4 = n (moles)
Here we are given four different gases ${ O }_{ 2 }$, ${ F }_{ 2 }$, ${ CH }_{ 4 }$ and ${ CO }_{ 2 }$. These are filled in four different flasks that have the same volume, pressure and temperature are also the same. So, therefore Avogadro’s law is applicable here. That means these all gases will have the same number of molecules.
We can say that ratio would be 1:1:1:1.

Therefore, we can conclude that the correct answer to this question is option B.

Note: In Avogadro’s law, we can replace “an equal number of molecules” with “an equal number of moles”, because every compound will have the same number of molecules in the given amount of moles.