# Question #01990

Feb 25, 2016

You may compare molecular masses, as all gasses have the same number of molecules in a certain volume. At STP 0 deg C and 1 Bar one mole of gas has a volume of 22.4 L.

#### Explanation:

Molar masses in $g / m o l$:
$N e = 20.18$
${N}_{2} = 2 \times 14.01 = 28.02$
$N {H}_{3} = 14.01 + 3 \times 1.008 = 17.03$
$C O = 12.01 + 16.00 = 28.01$

Ranking the densities from low to high:
$N {H}_{3} - N e - C O - {N}_{2}$

You could calculate the densities by dividing molar mass by molar volume, though this is not necessary to solve the problem.
E.g. $N {H}_{3} : \rho = \frac{17.03}{22.4} = 0.760 g / L = 0.760 k g / {m}^{3}$