Which one of the following is the correct $PV$ vs $P$ plot at constant temperature for an ideal gas? ($P$ and $V$ stand for pressure and volume of the gas respectively)

The variation of volume of an ideal gas with its number of moles $(n)$ is obtained as a graph at $300 \ K$ and $1 \ atm$ pressure. What is the slope of the graph?

The volume of $1 \ g$ of methane $(CH_4)$,ethane $(C_2H_6)$,propane $(C_3H_8)$,and butane $(C_4H_{10})$ is measured at $350 \ K$ and $1 \ atm$ pressure. What will be the volume of butane in $cm^3$?

Calculate the density of a gaseous mixture which consists of $3.01 \times 10^{24}$ molecules of $N_2$ and $32 \ g$ of $O_2$ gas at $3 \ atm$ pressure and $860 \ K$ temperature. (Given: $R = 1/12 \ atm \ L \ mol^{-1} \ K^{-1}$) ............. $g/L$

$A$ vacuum vessel of volume $1 \, dm^3$ is evacuated at a constant temperature of $-23 \, ^\circ C$ until the pressure drops to $7.6 \times 10^{-5} \, torr$. What is the number of molecules remaining in the vessel?

If $R = 0.082$,write it with its units and state the value with full precision.