Question

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

• A. $C{O}_2$
• B. $CO$
• C. $H_2$
• D. $NO$

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. So, the gas which will have the same mass is considered here.

We know that, molecular weight of $N_2=28$ $g$.
moles of $N_2=\text{moles of}X$ (they have same number of molecules).
This is only possible when they have the same molecular weight.
Molecular weight of $CO=28$ $g$.