Answer:
2nd one In my opinion....
I believe it is "empirical formula"
Answer:
20 g/mol
Explanation:
We can use <em>Graham’s Law of diffusion</em>:
The rate of diffusion (<em>r</em>) of a gas is inversely proportional to the square root of its molar mass (<em>M</em>).

If you have two gases, the ratio of their rates of diffusion is

Squaring both sides, we get

Solve for <em>M</em>₂:



Well, if you look at group 1 of the periodic table, you will notice a thrend. All elements in group 1 have 1 valence / outer electron. Then you look at period 2, 3, 4 and so on, you will see that the group number corresponds the number of valence/ outershell electrons. Hence, the group determines the electron(s) on the outershell.