Question

Which of the following gases is the heaviest? O2, CH4, CO2, Cl2 O2 CH4 CO2 Cl2
Which of the following gases diffuses the fastest?

O2, CH4, CO2, Cl2

O2
CH4
CO2
Cl2

Answer 1

CH4 is the heaviest gas in the above option

Answer 2

Answer: The heaviest gas is chlorine gas $Cl_2$.

The methane gas has lowest molar mass that is of 16 amu which means it will get diffuse fastest from the other enlisted gases.

Explanation:

1) The gas with highest molar mass will be considered as heaviest gas.

Molar mass of the $O_2$ = 32 amu

Molar mass of the $CH_4$ = 16 amu

Molar mass of the $CO_2$ = 44 amu

Molar mass of the $Cl_2$ = 71 amu

The heaviest gas is chlorine gas $Cl_2$.

2) Diffusion of the gas :

$\text{Diffusion rate of gas} \propto \frac{1}{\text{molar mass of the gas}}$ (Graham's law)

The gas with lowest value mass will get diffused fastest.

The methane gas has lowest molar mass that is of 16 amu which means it will get diffuse fastest from the other enlisted gases.