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.

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 $CO=28$ $g$.