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

If a gas expands from $20 \ cm^3$ to $50 \ cm^3$ at a constant temperature $(T)$ under a pressure of $1 \ atm$,what will be the final pressure?

The correct gas equation is:

The volume occupied by $1.8 \; g$ of water vapour at $374^{\circ} C$ and $1 \; bar$ pressure will be $....... \; L$ : [Use $R=0.083 \; bar \; L \; K^{-1} \; mol^{-1}$]

At what new pressure will $100 \ mL$ of a gas at a pressure of $720 \ mm$ occupy a volume of $84 \ mL$,keeping the temperature constant (in $mm$)?

In an experiment during the analysis of a carbon compound,$145 \ L$ of $H_2$ was collected at $760 \ mm \ Hg$ pressure and $27 \ ^oC$ temperature. The mass of $H_2$ is nearly $....... \ g$.