The use of hot air balloons for sports and meteorological observations is based on which of the following laws?

At a temperature of $27\,^oC$ and a pressure of $1\,atm$,the density of a gas is $d$. At constant pressure,at what temperature will its density become $0.75\,d$?

At $N.T.P.$,the density of a gas is $0.00356 \ g/mL$. What is the molecular mass of the gas?

At temperature $t \, ^oC$,the pressure exerted by $12 \, g$ of an ideal gas in a container of volume $V \, L$ is $1 \, atm$. When the temperature is increased by $10 \, ^oC$ without changing the volume,the pressure increases by $10 \%$. Find the temperature $t$ and volume $V$ in $L$. (Molar mass of the gas = $120 \, g/mol$)

If the absolute temperature of an ideal gas becomes double and the pressure becomes half,the volume of the gas would be:

$A$ gas occupies $11.2 \ dm^3$ at $105 \ kPa$. What is the volume if pressure is increased to $210 \ kPa$ (in $dm^3$)?