Astronauts use "Astronomical Unit" to measure the distance between planets in our solar system "only". To measure long distances like between 2 galaxies, they use "light years". One Astronomical Unit = Average distance between sun and earth which is equal to 149.6 million kilometers. Ping me if you have any doubt.
Answer:

Explanation:

if temperature is constant.

if we are comparing two gases,

Let chlorine be Gas 1 and ethane be Gas 2
Data:
M₁ = 70.91 g/mol
M₂ = 30.07 g/mol
Calculation

Answer:
D
Explanation:
31 / 2.8 = 11.0714286 L per mole of helium
3.5 / 4 = 0.875 moles
2.8 + 0.875 = 3.675 moles
11.0714286 x 3.675 = 40.6875 L
Common thing is that their outmost shell is completely filled with the electrons. They are inert gases.