Which one of the following graphs represents the behavior of an ideal gas at a constant temperature?

$A$ gas has a volume of $251 \,cm^3$ at $20^{\circ} C$ and a pressure of $78 \,cm$ of $Hg$. Find its volume at $NTP$. (in $\,cm^3$)

An ideal gas is initially at temperature $T$ and volume $V.$ Its volume is increased by $\Delta V$ due to an increase in temperature $\Delta T,$ pressure remaining constant. The quantity $\delta = \Delta V / (V \Delta T)$ varies with temperature as

$A$ gas of certain mass filled in a closed cylinder at a pressure of $3.23 \ kPa$ has a temperature of $50^{\circ} C$. The gas is now heated until its absolute temperature is doubled. The modified pressure is . . . . . . $Pa$.

$A$ monoatomic ideal gas of two moles is taken through a cyclic process starting from $1$ as shown. Given $\frac{V_2}{V_1} = 2$ and $\frac{V_4}{V_1} = 4$. The temperature at state $1$ is $T_1 = 27\,^oC$. Find the temperature at state $2$,i.e.,$T_2$ in $K$.

Calculate the volume of vapour of $1\,g$ of water at $1\,atm$ pressure.