Question

$10{\text{dm}}^3$ of $N_2$ gas and $10{\text{dm}}^3$ of gas $X$ at the same temperature contain the same number of molecules and have same mass. The gas $X$ is:

• A. $C{O}_2$
• B. $CO$
• C. $H_2$
• D. $N$

Answer 1

The correct option is B $CO$

It is given that the gases are at the same temperature and volume conditions and contain the same number of molecules. We know that, molecular weight of $N_2=28\text{amu}$
Therefore, moles of $N_2$ = moles of $X$ (they have same number of molecules)
This is only possible when they have the same molecular weight.
Molecular weight of $CO=28\text{amu}$