Which of the following expressions at constant pressure represents Charles's law?

Which of the following laws is followed by a hot air balloon used for sports and meteorology?

$A$ steel cylinder contains helium gas at $250 \, kPa$ pressure and $300 \, K$ temperature. The cylinder can withstand a maximum pressure of $1 \times 10^6 \, Pa$. The room in which the cylinder is placed catches fire. Predict whether the cylinder will burst before it melts. (Melting point of the cylinder = $1800 \, K$)

$0.5 \, mol$ of gas $A$ and $x \, mol$ of gas $B$ exert a pressure of $200 \, Pa$ in a container of volume $10 \, m^3$ at $1000 \, K$. Given $R$ is the gas constant in $J \, K^{-1} \, mol^{-1}$,$x$ is

Under what conditions does an ideal gas have maximum density?

Provide the different values and units of the universal gas constant $R$.