The density of air is higher at sea level. Which of the following laws explains this practical observation?

The following graph illustrates:

At $27^{\circ} C$ in a $10 \ L$ flask,$4.0 \ g$ of an ideal gaseous mixture containing $He$ (molar mass $4.0 \ g \ mol^{-1}$) and $Ne$ (molar mass $20 \ g \ mol^{-1}$) has a pressure of $1.23 \ atm$. What is the mass $\%$ of neon? $(R = 0.082 \ L \ atm \ K^{-1} \ mol^{-1})$

Containers $A$ and $B$ contain the same gas. If the pressure,volume,and temperature of container $A$ are all twice those of container $B$,what is the ratio of the number of molecules in $A$ to those in $B$?

What does the following graph represent?

$A$ certain mass of a gas occupies a volume of $250 \ mL$ at $2 \ atm$ pressure. Calculate the volume of the gas if the pressure is increased to $2.5 \ atm$ at a constant temperature. (in $mL$)