Determine the relative density of nitrogen in terms of argon.

The ratio of the mass of a certain volume of one gas to the mass of the same volume of another gas (taken under the same conditions) is called the density of the first gas according to the second and is denoted by the letter D:

D = M1: M2.

The consequence of this formula is:

M1 = M2 * D.

How to calculate the mass of gas
In these formulas, the “mass” of each gas is understood as its molecular weight M, which is calculated by adding the relative atomic masses of all the elements that make up the formula of this gas.

For example:

for hydrogen chloride gas: M (HCl) = Ar (H) + Ar (Cl) = 1 + 35.5 = 36.5;
for hydrogen gas: M (H2) = 2 * Ar (H) = 2 * 1 = 2;
for oxygen gas: M (O2) = 2 * Ar (O) = 2 * 16 = 32.
For all the above calculations, Ar (element) is understood as the value of the relative atomic mass of this element from the table of D.I. Mendeleev.

Density of nitrogen in argon
In order to calculate the density of one gas in another, you should remember the following rules:

simple gas molecules consist of two identical atoms: O2, H2, F2, N2, Cl2;
some other gases contain more atoms in the molecule: O3 (ozone), P4 (phosphorus), S8 (sulfur vapor, at low temperatures);
molecules of inert gases located in the eighth group of the D.I. Mendeleev, consist of one atom: He (helium), Ne (neon), Ar (argon), Kr (krypton), Xe (xenon), Rn (radon). For them, the concepts of “molecule” and “atom” are equivalent.
The average molecular weight of air is conventionally equal to 29.
Based on the foregoing, the density of nitrogen in argon is equal to:

D = M (N2): M (Ar) = 28:40 = 0.7.

We can also find the density of nitrogen in terms of hydrogen and air:

D = M (N2): M (H2) = 28: 2 = 14;

D = M (N2): M (air) = 28:29 = 0.97.

Correct answer: the density of nitrogen in argon is 0.7.