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

One mole of an ideal gas at $300 \ K$ is expanded isothermally from $1 \ L$ to $10 \ L$ volume. $\Delta U$ for this process is $....... \ J$ (Use $R = 8.314 \ J \ K^{-1} \ mol^{-1}$)

Calculate the density of $CO_2$ at $100\, ^oC$ and $800\, mm\, Hg$ of pressure in $g/L$.

$A$ syringe has a volume of $10.0 \text{ cm}^3$ at a pressure of $1 \text{ atm}$. If the end is sealed and the plunger is pushed down at a constant temperature, what will be the final volume when the pressure becomes $3.5 \text{ atm}$ (in $\text{ cm}^3$)?

At constant temperature and pressure,what is the volume of $n$ moles of different gases?

Volume of the air that will be expelled from a vessel of $300 \; cm^{3}$ when it is heated from $27 \; ^{\circ}C$ to $37 \; ^{\circ}C$ at the same pressure will be ........... $cm^{3}$