In the figure, the straight line B shows the expansion of an ideal gas of volume V and mass m at a constant pressure P. Which straight line shows the expansion for the same ideal gas if mass and pressure are doubled.

$\text{ Here, }n=\frac{\text{ mass of gas }}{\text{ molar mass }}=\frac{m}{M}$

$\Rightarrow \mathrm{PV}=\frac{\mathrm{mRT}}{\mathrm{M}}$

$\Rightarrow \mathrm{V}=\frac{\mathrm{mRT}}{\mathrm{MP}}$

From the above equation volume is directly proportional to temperature.
Comparing it with equation of straight line

$y=mx+c$

Here,

$\text{ slope }=\frac{\mathrm{mR}}{\mathrm{MP}}$

Similarly, slope for other gas with mass 2m and pressure 2P is

$=\frac{2\mathrm{m}\times \mathrm{R}}{\mathrm{M}\times 2\mathrm{P}}$

On solving,

it is same as slope of first gas (B).