Consider one mole of a gas in a closed vessel fitted with a movable piston. At constant temperature ( $T$ ), the pressure of the gas $(P)$ is increased gradually and the volume $(V)$ is noted. The resulting $P$ - $V$ isotherm (not drawn to scale) is given below.


The correct plot (not drawn to scale) of the number of moles of the substance in gas phase ( $n \mathrm{G})$ against $V$ or $P$ is:

• A

  
  
• Correct answer
  B

  
  
• C

  
  
• D

  
  

Hence, the correct answer is option: 'B'.